// https://github.com/code-423n4/2021-08-realitycards/blob/main/contracts/RCMarket.sol#L691 ==> simplified version
function calc(uint256 currentPrice) returns(uint256) {
    if (currentPrice == 0)
        return MIN_RENTAL_VALUE;
    return (currentPrice *(minimumPriceIncreasePercent + 100)) / 100;
}

function rentAllCards(uint256 _maxSumOfPrices) external override {
    ..
    uint256 _actualSumOfPrices = 0;
    for (uint256 i = 0; i < numberOfCards; i++) {
        _actualSumOfPrices += calc(card[i].cardPrice);   // no check for  (ownerOf(i) != msgSender()) {
    }
    require(_actualSumOfPrices <= _maxSumOfPrices, "Prices too high");

    for (uint256 i = 0; i < numberOfCards; i++) {
        if (ownerOf(i) != msgSender()) {
            uint256 _newPrice=calc(card[i].cardPrice);
            newRental(_newPrice, 0, address(0), i);
        }
    }
}
uint256 _actualSumOfPrices = 0;
for (uint256 i = 0; i < numberOfCards; i++) {
    if (ownerOf(i) != msgSender()) {              // extra if statement
        _actualSumOfPrices += calc(card[i].cardPrice);
    }
}
