import sys

def debug(x, table):
    for name, val in table.items():
        if x is val:
            print('DEBUG:{} -> {}'.format(name, val), file=sys.stderr)
            return None

def solve():
    Bs = set([int(i) for i in input().split()])
    ans = set(range(1, 10)) - Bs

    print(ans.pop())

if __name__ == '__main__':
    solve()