# import sys; input = sys.stdin.buffer.readline
# sys.setrecursionlimit(10**7)
from collections import defaultdict
con = 10 ** 9 + 7; INF = float("inf")

def getlist():
	return list(map(int, input().split()))

#処理内容
def main():
	B = getlist()
	L = [0] * 10
	for i in B:
		L[i - 1] = 1

	for i in range(10):
		if L[i] == 0:
			print(i + 1)



if __name__ == '__main__':
	main()