from itertools import *
from functools import *
from collections import *
from math import *
from heapq import *
import sys

input = sys.stdin.readline

A = list(map(int,input().split()))
if len(set(A)) == 1:
    print(A[0])
elif len(set(A)) == 2:
    c = Counter(A)
    for k,v in c.items():
        if v == 1:
            print(k)
else:
    print(6-sum(A))