total = 0
    summary = True
    for i in range(len(numbers)):
        while summary is True:
            if len(numbers) == 0:
                break
            elif numbers[0] != 0:
                total += int(numbers[0])
                numbers.remove(numbers[0])
            elif numbers[0] == 0:
                numbers.remove(numbers[0])
                summary = False
        while summary is False:
            if len(numbers) == 0:
                break
            elif numbers[0] != 0:
                total -= int(numbers[0])
                numbers.remove(numbers[0])
            elif numbers[0] == 0:
                numbers.remove(numbers[0])
                summary = True
    print(total)