from collections import Counter


def main():
    fruits = Counter(map(int, input().split()))
    match len(fruits):
        case 1:
            print(list(fruits.keys())[0])
        case 3:
            print(6 - sum(fruits.keys()))
        case 2:
            print(list(filter(lambda elm: fruits[elm] == 1, fruits))[0])


if __name__ == "__main__":
    main()