content: set the_file to choose file
  set sum to 0
  repeat with mass in paragraphs of (read the_file)
  	set sum to sum + (calculate_fuel for mass)
  end repeat
  return sum
  
  on calculate_fuel for mass
  	set fuel to mass div 3 - 2
  	if fuel is greater than 0 then
  		return fuel + (calculate_fuel for fuel)
  	else
  		return 0
  	end if
  end calculate_fuel