package main

import (
	"bufio"
	"fmt"
	"math"
	"os"
	"strconv"
	"strings"
)

func main() {
	defer out.Flush()
	for t := ScanInt(); t > 0; t-- {
		P(solve())
	}

}

var m map[int]bool

func solve() int {
	m = make(map[int]bool)
	n := ScanInt()
	a := ScanInts(n)

	for i := 1; i <= 1024; i++ {
		allFound := true
		for j := 0; j < n; j++ {
			if _, found := m[i^a[j]]; !found {
				allFound = false
				break
			}
		}

		if allFound {
			return i
		}
	}
	return -1
}

/*********************** I/O ***********************/
var in *bufio.Scanner
var out *bufio.Writer

func init() {
	in = bufio.NewScanner(os.Stdin)
	in.Buffer(make([]byte, 1024), int(1e+9))
	in.Split(bufio.ScanWords)
	out = bufio.NewWriter(os.Stdout)
}

func P(args ...interface{}) {
	print("\n", args...)
}

func PS(args ...interface{}) {
	print(" ", args...)
	print("\n", nil)
}

func print(seperator string, args ...interface{}) {
	for _, arg := range args {
		str := ""
		switch v := arg.(type) {
		case byte:
			str = string(v)
		case rune:
			str = string(v)
		case int:
			str = strconv.Itoa(v)
		case []int:
			sb := strings.Builder{}
			for i := 0; i < len(v); i++ {
				sb.WriteString(strconv.Itoa(v[i]) + " ")
			}
			str = sb.String()
		case int64:
			str = strconv.FormatInt(v, 10)
		case []int64:
			sb := strings.Builder{}
			for i := 0; i < len(v); i++ {
				sb.WriteString(strconv.FormatInt(v[i], 10) + " ")
			}
			str = sb.String()
		case string:
			str = v
		default:
			panic("invalid print arg: " + fmt.Sprintf("%v", arg))

		}
		out.WriteString(str + seperator)
	}
}

func ScanWord() string { in.Scan(); return in.Text() }
func ScanWords(n int) []string {
	s := make([]string, n)
	for i := 0; i < n; i++ {
		s[i] = ScanWord()
	}
	return s
}
func ScanInt() int { i, _ := strconv.Atoi(ScanWord()); return i }
func ScanInts(n int) []int {
	a := make([]int, n)
	for i := 0; i < n; i++ {
		a[i] = ScanInt()
		m[a[i]] = true
	}
	return a
}

func MnMx(args ...int) (int, int) {
	minVal, maxVal := math.MaxInt32, math.MinInt32
	for _, v := range args {
		if v < minVal {
			minVal = v
		}
		if v > maxVal {
			maxVal = v
		}
	}
	return minVal, maxVal
}
func Mn(args ...int) int { mn, _ := MnMx(args...); return mn }
func Mx(args ...int) int { _, mx := MnMx(args...); return mx }
func LCM(a, b int) int   { return a / GCD(a, b) * b }
func GCD(a, b int) int {
	if a == 0 {
		return b
	}
	return GCD(b%a, a)
}
func Abs(x int) int {
	if x < 0 {
		return -x
	}
	return x
}

package main

import (
	"bufio"
	"fmt"
	"math"
	"os"
	"strconv"
	"strings"
)

func main() {
	defer out.Flush()
	for t := ScanInt(); t > 0; t-- {
		P(solve())
	}

}

var m map[int]bool

func solve() int {
	n := ScanInt()
	a := ScanInts(n)

	//max := Mx(a...)

	for i := 1; i <= 1024; i++ {
		m := make(map[int]bool)
		for j := 0; j < n; j++ {
			m[a[j]^i] = true
		}

		allFound := true
		for j := 0; j < n; j++ {
			if _, found := m[a[j]]; !found {
				allFound = false
				break
			}
		}
		if allFound {
			return i
		}
	}
	return -1
}

/*********************** I/O ***********************/
var in *bufio.Scanner
var out *bufio.Writer

func init() {
	in = bufio.NewScanner(os.Stdin)
	in.Buffer(make([]byte, 1024), int(1e+9))
	in.Split(bufio.ScanWords)
	out = bufio.NewWriter(os.Stdout)
}

func P(args ...interface{}) {
	print("\n", args...)
}

func PS(args ...interface{}) {
	print(" ", args...)
	print("\n", nil)
}

func print(seperator string, args ...interface{}) {
	for _, arg := range args {
		str := ""
		switch v := arg.(type) {
		case byte:
			str = string(v)
		case rune:
			str = string(v)
		case int:
			str = strconv.Itoa(v)
		case []int:
			sb := strings.Builder{}
			for i := 0; i < len(v); i++ {
				sb.WriteString(strconv.Itoa(v[i]) + " ")
			}
			str = sb.String()
		case int64:
			str = strconv.FormatInt(v, 10)
		case []int64:
			sb := strings.Builder{}
			for i := 0; i < len(v); i++ {
				sb.WriteString(strconv.FormatInt(v[i], 10) + " ")
			}
			str = sb.String()
		case string:
			str = v
		default:
			panic("invalid print arg: " + fmt.Sprintf("%v", arg))

		}
		out.WriteString(str + seperator)
	}
}

func ScanWord() string { in.Scan(); return in.Text() }
func ScanWords(n int) []string {
	s := make([]string, n)
	for i := 0; i < n; i++ {
		s[i] = ScanWord()
	}
	return s
}
func ScanInt() int { i, _ := strconv.Atoi(ScanWord()); return i }
func ScanInts(n int) []int {
	a := make([]int, n)
	for i := 0; i < n; i++ {
		a[i] = ScanInt()
	}
	return a
}

func MnMx(args ...int) (int, int) {
	minVal, maxVal := math.MaxInt32, math.MinInt32
	for _, v := range args {
		if v < minVal {
			minVal = v
		}
		if v > maxVal {
			maxVal = v
		}
	}
	return minVal, maxVal
}
func Mn(args ...int) int { mn, _ := MnMx(args...); return mn }
func Mx(args ...int) int { _, mx := MnMx(args...); return mx }
func LCM(a, b int) int   { return a / GCD(a, b) * b }
func GCD(a, b int) int {
	if a == 0 {
		return b
	}
	return GCD(b%a, a)
}
func Abs(x int) int {
	if x < 0 {
		return -x
	}
	return x
}

package main

import (
	"bufio"
	. "fmt"
	"os"
	"strconv"
)

var (
	inn = bufio.NewScanner(os.Stdin)
	in  = bufio.NewReader(os.Stdin)
	out = bufio.NewWriter(os.Stdout)
)

func main() {
	defer out.Flush()
	inn.Buffer([]byte{}, 10000000)
	inn.Split(bufio.ScanWords)

	for tt := rd(); tt > 0; tt-- {
		n := rd()
		a := make([]int, n)
		cnt := [1024]int{}
		for i := range a {
			a[i] = rd()
			cnt[a[i]]++
		}
		for i := 1; i < 1024; i++ {
			tcnt := [1024]int{}
			for _, it := range a {
				tcnt[it^i]++
			}
			for j := range cnt {
				if cnt[j] != tcnt[j] {
					goto next
				}
			}
			Fprintln(out, i)
			goto nnext
		next:
		}
		Fprintln(out, -1)
	nnext:
	}
}

func max(a, b int) int {
	if a > b {
		return a
	}
	return b
}
func min(a, b int) int {
	if a < b {
		return a
	}
	return b
}
func min64(a, b int64) int64 {
	if a < b {
		return a
	}
	return b
}
func rd() (x int) {
	inn.Scan()
	data := inn.Bytes()
	x, _ = strconv.Atoi(string(data))
	return x
}
func rdll() (x int64) {
	inn.Scan()
	data := inn.Bytes()
	x, _ = strconv.ParseInt(string(data), 10, 64)
	return x
}
func rds() string {
	inn.Scan()
	return string(inn.Bytes())
}

package main

import (
	"bufio"
	"fmt"
	"log"
	"os"
	"sort"
)

func fastGetInt(b []byte) int {
	neg := false
	if b[0] == '-' {
		neg = true
		b = b[1:]
	}
	n := 0
	for _, v := range b {
		n = n*10 + int(v-'0')
	}
	if neg {
		return -n
	}
	return n
}

func equalSlice(s1 []int, s2 []int) bool {
	if len(s1) != len(s2) {
		return false
	}
	for x := 0; x < len(s1); x++ {
		if s1[x] != s2[x] {
			return false
		}
	}
	return true
}

//========== Implement Algorithm =======================
func solution(sl []int) {
	sort.Ints(sl)
	check := false
	for i := 1; i < 1040; i++ {
		newSl := make([]int, len(sl))
		for x := 0; x < len(sl); x++ {
			newSl[x] = sl[x] ^ i
		}
		sort.Ints(newSl)
		if equalSlice(newSl, sl) {
			fmt.Println(i)
			check = true
			break
		}
	}
	if !check {
		fmt.Println(-1)
	}
}

func main() {

	scanner := bufio.NewScanner(os.Stdin)

	//================== Variables used ====================
	var num int
	//======================================================

	//============== Get return value from File ============
	if len(os.Args) >= 2 {

		file, err := os.Open(os.Args[1])
		if err != nil {
			log.Fatalf("failed opening file: %s", err)
		}
		scanner = bufio.NewScanner(file)
		defer file.Close()

	}
	scanner.Split(bufio.ScanWords)
	//======================= I/O ==========================
	scanner.Scan()
	num = fastGetInt(scanner.Bytes())
	//======================================================
	for x := 0; x < num; x++ {
		scanner.Scan()
		a := fastGetInt(scanner.Bytes())
		sl := make([]int, a)
		for i := 0; i < a; i++ {
			scanner.Scan()
			sl[i] = fastGetInt(scanner.Bytes())
		}
		solution(sl)
	}
	//==================== OUTPUT ==========================

}

package main

import (
	"bufio"
	"fmt"
	"os"
)

func readInt(bytes []byte, from int, val *int) int {
	i := from
	sign := 1
	if bytes[i] == '-' {
		sign = -1
		i++
	}
	tmp := 0
	for i < len(bytes) && bytes[i] >= '0' && bytes[i] <= '9' {
		tmp = tmp*10 + int(bytes[i]-'0')
		i++
	}
	*val = tmp * sign
	return i
}

func readNum(reader *bufio.Reader) (a int) {
	bs, _ := reader.ReadBytes('\n')
	readInt(bs, 0, &a)
	return
}

func readTwoNums(reader *bufio.Reader) (a int, b int) {
	res := readNNums(reader, 2)
	a, b = res[0], res[1]
	return
}

func readThreeNums(reader *bufio.Reader) (a int, b int, c int) {
	res := readNNums(reader, 3)
	a, b, c = res[0], res[1], res[2]
	return
}

func readNNums(reader *bufio.Reader, n int) []int {
	res := make([]int, n)
	x := 0
	bs, _ := reader.ReadBytes('\n')
	for i := 0; i < n; i++ {
		for x < len(bs) && (bs[x] < '0' || bs[x] > '9') && bs[x] != '-' {
			x++
		}
		x = readInt(bs, x, &res[i])
	}
	return res
}

func readUint64(bytes []byte, from int, val *uint64) int {
	i := from

	var tmp uint64
	for i < len(bytes) && bytes[i] >= '0' && bytes[i] <= '9' {
		tmp = tmp*10 + uint64(bytes[i]-'0')
		i++
	}
	*val = tmp

	return i
}

func main() {
	reader := bufio.NewReader(os.Stdin)

	tc := readNum(reader)

	for tc > 0 {
		tc--
		n := readNum(reader)

		A := readNNums(reader, n)

		fmt.Println(solve(n, A))
	}
}

func solve(n int, A []int) int {
	if n%2 == 1 {
		return -1
	}
	cnt := make([]int, 1025)
	for k := 1; k < 1025; k++ {
		var can = true
		for j := 0; j < n; j++ {
			if A[j]^k >= 1024 {
				can = false
				break
			}
			cnt[A[j]]++
			cnt[A[j]^k]--
		}
		if !can {
			continue
		}
		for j := 0; j < 1025; j++ {
			if cnt[j] != 0 {
				can = false
				break
			}
		}
		if can {
			return k
		}
		for j := 0; j < 1025; j++ {
			cnt[j] = 0
		}
	}
	return -1
}

package main

import (
	"bufio"
	"fmt"
	"os"
	"io"
)

// (c) Dmitriy Blokhin (sv.dblokhin@gmail.com)
var input io.Reader

func main() {
	var (
		T int
	)

	//f, _ := os.Open("input.txt")
	//input := bufio.NewReader(f)
	input = bufio.NewReader(os.Stdin)
	fmt.Fscan(input, &T)
	for i := 0; i < T; i++ {
		solver()
	}
}

func solver() {
	var n int
	table := make(map[int]bool)
	fmt.Fscan(input, &n)
	s := make([]int, n)
	for i := 0; i < n; i++ {
		fmt.Fscan(input, &s[i])
		table[s[i]] = true
	}

	worker:
	for k := 1; k <= 1024; k++ {
		for _, v := range s {
			vn := v ^ k
			if !(v != vn && table[vn]) {continue worker}
		}
		fmt.Println(k)
		return
	}
	fmt.Println(-1)
}

package main

import (
	"bufio"
	"fmt"
	"io"
	"os"
	"sort"
  "strings"
  "strconv"
  "math"
  "reflect"
)

var reader = NewWordScanner(os.Stdin)
var writer = NewBufferedWriter(os.Stdout)

func main() {
	defer writer.Flush()
	t := reader.NextInt64()
	for ; t > 0; t-- {
		n:= reader.NextInt()
		aa := make([]int, n)
		// hm:=make(map[int]bool)
		max:=0
		for i := 0; i < n; i++ {
			aa[i]=reader.NextInt()
			if(aa[i]>max){
				max=aa[i]
			}
		}
		sort.Ints(aa)
		sol(aa, n,max)
	}
}

func sol(aa []int, n int, max int)  {
	slc:=make([]int,n)
	copy(slc,aa)
	for i:=1;i<=1024;i++ {
		for j:=0;j<n;j++{
			slc[j]=slc[j]^i
		}
		sort.Ints(slc)
		if(reflect.DeepEqual(slc, aa)){
			writer.Printf("%d\n",i)
			return;
		}else{
			copy(slc,aa)
			// fmt.Println(slc)
		}
	}
  writer.Printf("-1\n")
}

/*********************** I/O ***********************/

type BufferedWriter interface {
	Printf(format string, a ...interface{})
	Flush()
}

type writerImpl struct {
	*bufio.Writer
}

func NewBufferedWriter(writer io.Writer) BufferedWriter {
	return &writerImpl{Writer: bufio.NewWriter(writer)}
}

func (impl *writerImpl) Printf(f string, a ...interface{}) {
	fmt.Fprintf(impl.Writer, f, a...)
}

func (impl *writerImpl) Flush() {
	impl.Writer.Flush()
}

type WordScanner interface {
	NextInt() int
	NextInt64() int64
	NextString() string
}

type wordScannerImpl struct {
	*bufio.Scanner
}

func NewWordScanner(reader io.Reader) WordScanner {
	s := bufio.NewScanner(reader)
	s.Split(bufio.ScanWords)
	// adjust the following size as needed
	// 2 << 17 is good enough to scan strings of len 2*10^5
	// it could go as high as 2 << 26 before cf judge breaks
	size := 2 << 20
	buf := make([]byte, size)
	s.Buffer(buf, size)
	return &wordScannerImpl{Scanner: s}
}

func (impl *wordScannerImpl) NextInt() int {
	impl.Scan()
	bb := impl.Bytes()
	i := 0
	if bb[0] == '-' {
		for _, b := range bb[1:] {
			i *= 10
			i -= int(b - '0')
		}
		return i
	}
	for _, b := range bb {
		i *= 10
		i += int(b - '0')
	}
	return i
}

func (impl *wordScannerImpl) NextInt64() int64 {
	impl.Scan()
	bb := impl.Bytes()
	i := int64(0)
	if bb[0] == '-' {
		for _, b := range bb[1:] {
			i *= 10
			i -= int64(b - '0')
		}
		return i
	}
	for _, b := range bb {
		i *= 10
		i += int64(b - '0')
	}
	return i
}

func (impl *wordScannerImpl) NextString() string {
	impl.Scan()
	return impl.Text()
}
/*********************** Utils ***********************/

func S(v interface{}) string { return fmt.Sprintf("%v", v) }
func SArr(a []int) string {
	sb := strings.Builder{}
	sb.Grow(len(a) * 9)
	for i := range a {
		sb.WriteString(strconv.Itoa(a[i]) + " ")
	}
	return sb.String()
}
func SArr64(a []int64) string {
	sb := strings.Builder{}
	sb.Grow(len(a) * 9)
	for i := range a {
		sb.WriteString(strconv.FormatInt(a[i], 10) + " ")
	}
	return sb.String()
}
func MnMx(args ...int64) (int64, int64) {
	minVal, maxVal := int64(math.MaxInt64), int64(math.MinInt64)
	for _, v := range args {
		if v < minVal {
			minVal = v
		}
		if v > maxVal {
			maxVal = v
		}
	}
	return minVal, maxVal
}
func Mn(args ...int64) int64 { mn, _ := MnMx(args...); return mn }
func Mx(args ...int64) int64 { _, mx := MnMx(args...); return mx }
func LCM(a, b int64) int64   { return a / GCD(a, b) * b }
func GCD(a, b int64) int64 {
	if a == 0 {
		return b
	}
	return GCD(b%a, a)
}
func sortInt64Slice(a []int64) { sort.Slice(a, func(i, j int) bool { return a[i] < a[j] }) }
func abs(x int64) int64 {
	if x < 0 {
		return -x
	}
	return x
}

package main

import (
	"bufio"
	"fmt"
	"os"
	"sort"
	"strconv"
)

func main() {
	t := nextInt()
	for i := 0; i < t; i++ {
		n := nextInt()
		s := nextInts(n)
		fmt.Println(solve(n, s))
	}
}

func solve(n int, s []int) int {
	if n == 1 {
		return -1
	}

	sort.Ints(s)

	sumXor := 0
	sumOr := 0
	for i := 0; i < len(s); i++ {
		sumXor ^= s[i]
		sumOr |= s[i]
	}
	for t := 1; t <= sumOr; t++ {
		if t&sumOr != t {
			continue
		}
		if check(sumXor, t, s) {
			return t
		}
	}
	return -1
}

func check(sumXor, t int, s []int) bool {
	sum := 0
	products := make([]int, len(s))
	for i := 0; i < len(s); i++ {
		p := (s[i] ^ t)
		sum ^= p
		products[i] = p
	}
	if sum != sumXor {
		return false
	}

	sort.Ints(products)
	for i := 0; i < len(s); i++ {
		if products[i] != s[i] {
			return false
		}
	}
	return true
}

var sc = bufio.NewScanner(os.Stdin)

func init() {
	sc.Buffer(make([]byte, 256), 1e9)
	sc.Split(bufio.ScanWords)
}

func next() string {
	sc.Scan()
	return sc.Text()
}

func nextInt() int {
	a, _ := strconv.Atoi(next())
	return a
}

func nextInts(n int) []int {
	ret := make([]int, n)
	for i := 0; i < n; i++ {
		ret[i] = nextInt()
	}
	return ret
}

/*
URL:
https://codeforces.com/contest/1362/problem/B
*/

package main

import (
	"bufio"
	"errors"
	"fmt"
	"io"
	"math"
	"os"
	"sort"
	"strconv"
)

/********** FAU standard libraries **********/

//fmt.Sprintf("%b\n", 255) 	// binary expression

/********** I/O usage **********/

//str := ReadString()
//i := ReadInt()
//X := ReadIntSlice(n)
//S := ReadRuneSlice()
//a := ReadFloat64()
//A := ReadFloat64Slice(n)

//str := ZeroPaddingRuneSlice(num, 32)
//str := PrintIntsLine(X...)

/*******************************************************************/

const (
	// General purpose
	MOD          = 1000000000 + 7
	ALPHABET_NUM = 26
	INF_INT64    = math.MaxInt64
	INF_BIT60    = 1 << 60
	INF_INT32    = math.MaxInt32
	INF_BIT30    = 1 << 30
	NIL          = -1

	// for dijkstra, prim, and so on
	WHITE = 0
	GRAY  = 1
	BLACK = 2
)

func init() {
	// bufio.ScanWords <---> bufio.ScanLines
	ReadString = newReadString(os.Stdin, bufio.ScanWords)
	stdout = bufio.NewWriter(os.Stdout)
}

var (
	t int

	n int
	S []int
)

func main() {
	t = ReadInt()
	for i := 0; i < t; i++ {
		n = ReadInt()
		S = ReadIntSlice(n)

		solve()
	}
}

func solve() {
	// for i := 0; i < n; i++ {
	// 	PrintfDebug("%2d: %s\n", S[i], string(ZeroPaddingRuneSlice(S[i], 10)))
	// }
	// PrintfDebug("\n")
	sort.Sort(sort.IntSlice(S))

	for k := 1; k < 1024; k++ {
		T := []int{}
		for i := 0; i < n; i++ {
			c := k ^ S[i]
			T = append(T, c)
		}

		sort.Sort(sort.IntSlice(T))
		if isSame(S, T) {
			fmt.Println(k)
			return
		}
	}
	fmt.Println(-1)
}

func isSame(A, B []int) bool {
	for i := 0; i < n; i++ {
		if A[i] != B[i] {
			return false
		}
	}
	return true
}

/*******************************************************************/

/*********** I/O ***********/

var (
	// ReadString returns a WORD string.
	ReadString func() string
	stdout     *bufio.Writer
)

func newReadString(ior io.Reader, sf bufio.SplitFunc) func() string {
	r := bufio.NewScanner(ior)
	r.Buffer(make([]byte, 1024), int(1e+9)) // for Codeforces
	r.Split(sf)

	return func() string {
		if !r.Scan() {
			panic("Scan failed")
		}
		return r.Text()
	}
}

// ReadInt returns an integer.
func ReadInt() int {
	return int(readInt64())
}
func ReadInt2() (int, int) {
	return int(readInt64()), int(readInt64())
}
func ReadInt3() (int, int, int) {
	return int(readInt64()), int(readInt64()), int(readInt64())
}
func ReadInt4() (int, int, int, int) {
	return int(readInt64()), int(readInt64()), int(readInt64()), int(readInt64())
}

// ReadInt64 returns as integer as int64.
func ReadInt64() int64 {
	return readInt64()
}
func ReadInt64_2() (int64, int64) {
	return readInt64(), readInt64()
}
func ReadInt64_3() (int64, int64, int64) {
	return readInt64(), readInt64(), readInt64()
}
func ReadInt64_4() (int64, int64, int64, int64) {
	return readInt64(), readInt64(), readInt64(), readInt64()
}

func readInt64() int64 {
	i, err := strconv.ParseInt(ReadString(), 0, 64)
	if err != nil {
		panic(err.Error())
	}
	return i
}

// ReadIntSlice returns an integer slice that has n integers.
func ReadIntSlice(n int) []int {
	b := make([]int, n)
	for i := 0; i < n; i++ {
		b[i] = ReadInt()
	}
	return b
}

// ReadInt64Slice returns as int64 slice that has n integers.
func ReadInt64Slice(n int) []int64 {
	b := make([]int64, n)
	for i := 0; i < n; i++ {
		b[i] = ReadInt64()
	}
	return b
}

// ReadFloat64 returns an float64.
func ReadFloat64() float64 {
	return float64(readFloat64())
}

func readFloat64() float64 {
	f, err := strconv.ParseFloat(ReadString(), 64)
	if err != nil {
		panic(err.Error())
	}
	return f
}

// ReadFloatSlice returns an float64 slice that has n float64.
func ReadFloat64Slice(n int) []float64 {
	b := make([]float64, n)
	for i := 0; i < n; i++ {
		b[i] = ReadFloat64()
	}
	return b
}

// ReadRuneSlice returns a rune slice.
func ReadRuneSlice() []rune {
	return []rune(ReadString())
}

/*********** Debugging ***********/

// ZeroPaddingRuneSlice returns binary expressions of integer n with zero padding.
// For debugging use.
func ZeroPaddingRuneSlice(n, digitsNum int) []rune {
	sn := fmt.Sprintf("%b", n)

	residualLength := digitsNum - len(sn)
	if residualLength <= 0 {
		return []rune(sn)
	}

	zeros := make([]rune, residualLength)
	for i := 0; i < len(zeros); i++ {
		zeros[i] = '0'
	}

	res := []rune{}
	res = append(res, zeros...)
	res = append(res, []rune(sn)...)

	return res
}

// Strtoi is a wrapper of strconv.Atoi().
// If strconv.Atoi() returns an error, Strtoi calls panic.
func Strtoi(s string) int {
	if i, err := strconv.Atoi(s); err != nil {
		panic(errors.New("[argument error]: Strtoi only accepts integer string"))
	} else {
		return i
	}
}

// PrintIntsLine returns integers string delimited by a space.
func PrintIntsLine(A ...int) string {
	res := []rune{}

	for i := 0; i < len(A); i++ {
		str := strconv.Itoa(A[i])
		res = append(res, []rune(str)...)

		if i != len(A)-1 {
			res = append(res, ' ')
		}
	}

	return string(res)
}

// PrintIntsLine returns integers string delimited by a space.
func PrintInts64Line(A ...int64) string {
	res := []rune{}

	for i := 0; i < len(A); i++ {
		str := strconv.FormatInt(A[i], 10) // 64bit int version
		res = append(res, []rune(str)...)

		if i != len(A)-1 {
			res = append(res, ' ')
		}
	}

	return string(res)
}

// PrintfDebug is wrapper of fmt.Fprintf(os.Stderr, format, a...)
func PrintfDebug(format string, a ...interface{}) {
	fmt.Fprintf(os.Stderr, format, a...)
}

// PrintfBufStdout is function for output strings to buffered os.Stdout.
// You may have to call stdout.Flush() finally.
func PrintfBufStdout(format string, a ...interface{}) {
	fmt.Fprintf(stdout, format, a...)
}

package main

import "fmt"

func main() {
	var nTest int
	fmt.Scan(&nTest)

	for t := 0; t < nTest; t++ {
		var n int
		fmt.Scan(&n)
		var a [1025]int

		for i := 0; i < n; i++ {
			fmt.Scan(&a[i])
		}

		var cnt [1025]int
		for i := 0; i < n; i++ {
			for j := 0; j < n; j++ {
				cnt[a[i]^a[j]]++
			}
		}

		hasSolution := false
		for i := 1; i < 1025; i++ {
			if cnt[i] == n {
				fmt.Println(i)
				hasSolution = true
				break
			}
		}

		if !hasSolution {
			fmt.Println(-1)
		}
	}
}

package main

import (
	"bufio"
	"fmt"
	"os"
)

func readInt(bytes []byte, from int, val *int) int {
	i := from
	sign := 1
	if bytes[i] == '-' {
		sign = -1
		i++
	}
	tmp := 0
	for i < len(bytes) && bytes[i] >= '0' && bytes[i] <= '9' {
		tmp = tmp*10 + int(bytes[i]-'0')
		i++
	}
	*val = tmp * sign
	return i
}

func readNum(reader *bufio.Reader) (a int) {
	bs, _ := reader.ReadBytes('\n')
	readInt(bs, 0, &a)
	return
}

func readTwoNums(reader *bufio.Reader) (a int, b int) {
	res := readNNums(reader, 2)
	a, b = res[0], res[1]
	return
}

func readThreeNums(reader *bufio.Reader) (a int, b int, c int) {
	res := readNNums(reader, 3)
	a, b, c = res[0], res[1], res[2]
	return
}

func readNNums(reader *bufio.Reader, n int) []int {
	res := make([]int, n)
	x := 0
	bs, _ := reader.ReadBytes('\n')
	for i := 0; i < n; i++ {
		for x < len(bs) && (bs[x] < '0' || bs[x] > '9') && bs[x] != '-' {
			x++
		}
		x = readInt(bs, x, &res[i])
	}
	return res
}

func readUint64(bytes []byte, from int, val *uint64) int {
	i := from

	var tmp uint64
	for i < len(bytes) && bytes[i] >= '0' && bytes[i] <= '9' {
		tmp = tmp*10 + uint64(bytes[i]-'0')
		i++
	}
	*val = tmp

	return i
}

func main() {
	reader := bufio.NewReader(os.Stdin)

	tc := readNum(reader)

	for tc > 0 {
		tc--
		n := readNum(reader)

		A := readNNums(reader, n)

		fmt.Println(solve(n, A))
	}
}

func solve(n int, A []int) int {
	if n%2 == 1 {
		return -1
	}

	var res int
	var res2 int = -1
	for i := 0; i < 11; i++ {
		var cnt int
		for j := 0; j < n; j++ {
			cnt += (A[j] >> i) & 1
		}
		cnt2 := n - cnt
		//如果put 1, 0 ^ 1 => 1, 1 ^ 1 => 0
		//如果put 0，0 ^ 0 => 0, 1 ^ 0 => 1
		if cnt == cnt2 && res2 < 0 {
			res2 = 1 << i
		}
		if cnt&1 == 0 && cnt2&1 == 0 {
			// can put 0 here
		} else {
			// have to put 1 here
			if cnt != cnt2 {
				return -1
			}
			res |= 1 << i
		}
	}

	if res == 0 {
		res = res2
	}

	if res < 0 {
		return -1
	}

	cnt := make([]int, 1025)

	for i := 0; i < n; i++ {
		cnt[A[i]]++
		cnt[res^A[i]]--
	}

	for i := 0; i < 1025; i++ {
		if cnt[i] != 0 {
			return -1
		}
	}

	return res
}

package main

import (
	"bufio"
	"fmt"
	"os"
)

func readInt(bytes []byte, from int, val *int) int {
	i := from
	sign := 1
	if bytes[i] == '-' {
		sign = -1
		i++
	}
	tmp := 0
	for i < len(bytes) && bytes[i] >= '0' && bytes[i] <= '9' {
		tmp = tmp*10 + int(bytes[i]-'0')
		i++
	}
	*val = tmp * sign
	return i
}

func readNum(reader *bufio.Reader) (a int) {
	bs, _ := reader.ReadBytes('\n')
	readInt(bs, 0, &a)
	return
}

func readTwoNums(reader *bufio.Reader) (a int, b int) {
	res := readNNums(reader, 2)
	a, b = res[0], res[1]
	return
}

func readThreeNums(reader *bufio.Reader) (a int, b int, c int) {
	res := readNNums(reader, 3)
	a, b, c = res[0], res[1], res[2]
	return
}

func readNNums(reader *bufio.Reader, n int) []int {
	res := make([]int, n)
	x := 0
	bs, _ := reader.ReadBytes('\n')
	for i := 0; i < n; i++ {
		for x < len(bs) && (bs[x] < '0' || bs[x] > '9') && bs[x] != '-' {
			x++
		}
		x = readInt(bs, x, &res[i])
	}
	return res
}

func readUint64(bytes []byte, from int, val *uint64) int {
	i := from

	var tmp uint64
	for i < len(bytes) && bytes[i] >= '0' && bytes[i] <= '9' {
		tmp = tmp*10 + uint64(bytes[i]-'0')
		i++
	}
	*val = tmp

	return i
}

func main() {
	reader := bufio.NewReader(os.Stdin)

	tc := readNum(reader)

	for tc > 0 {
		tc--
		n := readNum(reader)

		A := readNNums(reader, n)

		fmt.Println(solve(n, A))
	}
}

func solve(n int, A []int) int {
	if n%2 == 1 {
		return -1
	}
	cnt := make([]int, 1025)
	for i := 1; i < n; i++ {
		k := A[i] ^ A[0]
		if k >= 1024 {
			continue
		}
		var can = true
		for j := 0; j < n; j++ {
			if A[j]^k >= 1024 {
				can = false
				break
			}
			cnt[A[j]]++
			cnt[A[j]^k]--
		}
		if !can {
			continue
		}
		for j := 0; j < 1025; j++ {
			if cnt[j] != 0 {
				can = false
				break
			}
		}
		if can {
			return k
		}
		for j := 0; j < 1025; j++ {
			cnt[j] = 0
		}
	}
	return -1
}

package main

import (
	"bufio"
	"fmt"
	"io"
	"os"
	"sort"
  "strings"
  "strconv"
  "math"
  "reflect"
)

var reader = NewWordScanner(os.Stdin)
var writer = NewBufferedWriter(os.Stdout)

func main() {
	defer writer.Flush()
	t := reader.NextInt64()
	for ; t > 0; t-- {
		n:= reader.NextInt()
		aa := make([]int, n)
		// hm:=make(map[int]bool)
		max:=0
		for i := 0; i < n; i++ {
			aa[i]=reader.NextInt()
			if(aa[i]>max){
				max=aa[i]
			}
		}
		sort.Ints(aa)
		sol(aa, n,max)
	}
}

func sol(aa []int, n int, max int)  {
	slc:=make([]int,n)
	copy(slc,aa)
	for i:=1;i<=max;i++ {
		for j:=0;j<n;j++{
			slc[j]=slc[j]^i
		}
		sort.Ints(slc)
		if(reflect.DeepEqual(slc, aa)){
			writer.Printf("%d\n",i)
			return;
		}else{
			copy(slc,aa)
		}
	}
  writer.Printf("-1\n")
}

/*********************** I/O ***********************/

type BufferedWriter interface {
	Printf(format string, a ...interface{})
	Flush()
}

type writerImpl struct {
	*bufio.Writer
}

func NewBufferedWriter(writer io.Writer) BufferedWriter {
	return &writerImpl{Writer: bufio.NewWriter(writer)}
}

func (impl *writerImpl) Printf(f string, a ...interface{}) {
	fmt.Fprintf(impl.Writer, f, a...)
}

func (impl *writerImpl) Flush() {
	impl.Writer.Flush()
}

type WordScanner interface {
	NextInt() int
	NextInt64() int64
	NextString() string
}

type wordScannerImpl struct {
	*bufio.Scanner
}

func NewWordScanner(reader io.Reader) WordScanner {
	s := bufio.NewScanner(reader)
	s.Split(bufio.ScanWords)
	// adjust the following size as needed
	// 2 << 17 is good enough to scan strings of len 2*10^5
	// it could go as high as 2 << 26 before cf judge breaks
	size := 2 << 20
	buf := make([]byte, size)
	s.Buffer(buf, size)
	return &wordScannerImpl{Scanner: s}
}

func (impl *wordScannerImpl) NextInt() int {
	impl.Scan()
	bb := impl.Bytes()
	i := 0
	if bb[0] == '-' {
		for _, b := range bb[1:] {
			i *= 10
			i -= int(b - '0')
		}
		return i
	}
	for _, b := range bb {
		i *= 10
		i += int(b - '0')
	}
	return i
}

func (impl *wordScannerImpl) NextInt64() int64 {
	impl.Scan()
	bb := impl.Bytes()
	i := int64(0)
	if bb[0] == '-' {
		for _, b := range bb[1:] {
			i *= 10
			i -= int64(b - '0')
		}
		return i
	}
	for _, b := range bb {
		i *= 10
		i += int64(b - '0')
	}
	return i
}

func (impl *wordScannerImpl) NextString() string {
	impl.Scan()
	return impl.Text()
}
/*********************** Utils ***********************/

func S(v interface{}) string { return fmt.Sprintf("%v", v) }
func SArr(a []int) string {
	sb := strings.Builder{}
	sb.Grow(len(a) * 9)
	for i := range a {
		sb.WriteString(strconv.Itoa(a[i]) + " ")
	}
	return sb.String()
}
func SArr64(a []int64) string {
	sb := strings.Builder{}
	sb.Grow(len(a) * 9)
	for i := range a {
		sb.WriteString(strconv.FormatInt(a[i], 10) + " ")
	}
	return sb.String()
}
func MnMx(args ...int64) (int64, int64) {
	minVal, maxVal := int64(math.MaxInt64), int64(math.MinInt64)
	for _, v := range args {
		if v < minVal {
			minVal = v
		}
		if v > maxVal {
			maxVal = v
		}
	}
	return minVal, maxVal
}
func Mn(args ...int64) int64 { mn, _ := MnMx(args...); return mn }
func Mx(args ...int64) int64 { _, mx := MnMx(args...); return mx }
func LCM(a, b int64) int64   { return a / GCD(a, b) * b }
func GCD(a, b int64) int64 {
	if a == 0 {
		return b
	}
	return GCD(b%a, a)
}
func sortInt64Slice(a []int64) { sort.Slice(a, func(i, j int) bool { return a[i] < a[j] }) }
func abs(x int64) int64 {
	if x < 0 {
		return -x
	}
	return x
}

package main

import "fmt"

func main() {
	var nTest int
	fmt.Scanf("%d\n", &nTest)

	for t := 0; t < nTest; t++ {
		var n int
		fmt.Scanf("%d\n", &n)
		var a [1025]int

		for i := 0; i < n; i++ {
			fmt.Scanf("%d", &a[i])
		}

		var cnt [1025]int
		for i := 0; i < n; i++ {
			for j := 0; j < n; j++ {
				cnt[a[i]^a[j]]++
			}
		}

		hasSolution := false
		for i := 1; i < 1025; i++ {
			if cnt[i] == n {
				fmt.Println(i)
				hasSolution = true
				break
			}
		}

		if !hasSolution {
			fmt.Println(-1)
		}
	}
}

package main

import (
	"bufio"
	"fmt"
	"math"
	"os"
	"strconv"
	"strings"
)

func main() {
	defer out.Flush()
	for t := ScanInt(); t > 0; t-- {
		P(solve())
	}

}

var m map[int]bool

func solve() int {
	n := ScanInt()
	a := ScanInts(n)

	max := Mx(a...)

	for i := 1; i <= max; i++ {
		m := make(map[int]bool)
		for j := 0; j < n; j++ {
			m[a[j]^i] = true
		}

		allFound := true
		for j := 0; j < n; j++ {
			if _, found := m[a[j]]; !found {
				allFound = false
				break
			}
		}
		if allFound {
			return i
		}
	}
	return -1
}

/*********************** I/O ***********************/
var in *bufio.Scanner
var out *bufio.Writer

func init() {
	in = bufio.NewScanner(os.Stdin)
	in.Buffer(make([]byte, 1024), int(1e+9))
	in.Split(bufio.ScanWords)
	out = bufio.NewWriter(os.Stdout)
}

func P(args ...interface{}) {
	print("\n", args...)
}

func PS(args ...interface{}) {
	print(" ", args...)
	print("\n", nil)
}

func print(seperator string, args ...interface{}) {
	for _, arg := range args {
		str := ""
		switch v := arg.(type) {
		case byte:
			str = string(v)
		case rune:
			str = string(v)
		case int:
			str = strconv.Itoa(v)
		case []int:
			sb := strings.Builder{}
			for i := 0; i < len(v); i++ {
				sb.WriteString(strconv.Itoa(v[i]) + " ")
			}
			str = sb.String()
		case int64:
			str = strconv.FormatInt(v, 10)
		case []int64:
			sb := strings.Builder{}
			for i := 0; i < len(v); i++ {
				sb.WriteString(strconv.FormatInt(v[i], 10) + " ")
			}
			str = sb.String()
		case string:
			str = v
		default:
			panic("invalid print arg: " + fmt.Sprintf("%v", arg))

		}
		out.WriteString(str + seperator)
	}
}

func ScanWord() string { in.Scan(); return in.Text() }
func ScanWords(n int) []string {
	s := make([]string, n)
	for i := 0; i < n; i++ {
		s[i] = ScanWord()
	}
	return s
}
func ScanInt() int { i, _ := strconv.Atoi(ScanWord()); return i }
func ScanInts(n int) []int {
	a := make([]int, n)
	for i := 0; i < n; i++ {
		a[i] = ScanInt()
	}
	return a
}

func MnMx(args ...int) (int, int) {
	minVal, maxVal := math.MaxInt32, math.MinInt32
	for _, v := range args {
		if v < minVal {
			minVal = v
		}
		if v > maxVal {
			maxVal = v
		}
	}
	return minVal, maxVal
}
func Mn(args ...int) int { mn, _ := MnMx(args...); return mn }
func Mx(args ...int) int { _, mx := MnMx(args...); return mx }
func LCM(a, b int) int   { return a / GCD(a, b) * b }
func GCD(a, b int) int {
	if a == 0 {
		return b
	}
	return GCD(b%a, a)
}
func Abs(x int) int {
	if x < 0 {
		return -x
	}
	return x
}

package main

import (
	"bufio"
	"fmt"
	"math"
	"os"
	"strconv"
	"strings"
)

func main() {
	defer out.Flush()
	for t := ScanInt(); t > 0; t-- {
		P(solve())
	}

}

var m map[int]bool

func solve() int {
	m = make(map[int]bool)
	n := ScanInt()
	a := ScanInts(n)

	for i := 1; i <= 1024; i++ {
		allFound := true
		for j := 0; j < n; j++ {
			if _, found := m[a[j]]; !found {
				allFound = false
				break
			}
		}

		if allFound {
			return i
		}
	}
	return -1
}

/*********************** I/O ***********************/
var in *bufio.Scanner
var out *bufio.Writer

func init() {
	in = bufio.NewScanner(os.Stdin)
	in.Buffer(make([]byte, 1024), int(1e+9))
	in.Split(bufio.ScanWords)
	out = bufio.NewWriter(os.Stdout)
}

func P(args ...interface{}) {
	print("\n", args...)
}

func PS(args ...interface{}) {
	print(" ", args...)
	print("\n", nil)
}

func print(seperator string, args ...interface{}) {
	for _, arg := range args {
		str := ""
		switch v := arg.(type) {
		case byte:
			str = string(v)
		case rune:
			str = string(v)
		case int:
			str = strconv.Itoa(v)
		case []int:
			sb := strings.Builder{}
			for i := 0; i < len(v); i++ {
				sb.WriteString(strconv.Itoa(v[i]) + " ")
			}
			str = sb.String()
		case int64:
			str = strconv.FormatInt(v, 10)
		case []int64:
			sb := strings.Builder{}
			for i := 0; i < len(v); i++ {
				sb.WriteString(strconv.FormatInt(v[i], 10) + " ")
			}
			str = sb.String()
		case string:
			str = v
		default:
			panic("invalid print arg: " + fmt.Sprintf("%v", arg))

		}
		out.WriteString(str + seperator)
	}
}

func ScanWord() string { in.Scan(); return in.Text() }
func ScanWords(n int) []string {
	s := make([]string, n)
	for i := 0; i < n; i++ {
		s[i] = ScanWord()
	}
	return s
}
func ScanInt() int { i, _ := strconv.Atoi(ScanWord()); return i }
func ScanInts(n int) []int {
	a := make([]int, n)
	for i := 0; i < n; i++ {
		a[i] = ScanInt()
		m[a[i]] = true
	}
	return a
}

func MnMx(args ...int) (int, int) {
	minVal, maxVal := math.MaxInt32, math.MinInt32
	for _, v := range args {
		if v < minVal {
			minVal = v
		}
		if v > maxVal {
			maxVal = v
		}
	}
	return minVal, maxVal
}
func Mn(args ...int) int { mn, _ := MnMx(args...); return mn }
func Mx(args ...int) int { _, mx := MnMx(args...); return mx }
func LCM(a, b int) int   { return a / GCD(a, b) * b }
func GCD(a, b int) int {
	if a == 0 {
		return b
	}
	return GCD(b%a, a)
}
func Abs(x int) int {
	if x < 0 {
		return -x
	}
	return x
}