import sys
import math
import heapq
from collections import deque, Counter, defaultdict
from sys import stdin



INF = 10 ** 7
int1 = lambda x: int(x) - 1
stinput = lambda: stdin.readline()[:-1]
ii = lambda: int(stinput())  # int input
mi = lambda: map(int, stdin.readline().split())  # map input (int)
li = lambda: list(mi())  # list input (int)
mi1 = lambda: map(int1, stdin.readline().split())  # map input (int)-1
li1 = lambda: list(mi1())  # list input (int)-1
mis = lambda: map(str, stdin.readline().split())  # map input (string)
lis = lambda: list(mis())  # list input (string)


buy = li()
ans = set(range(4))
dd = defaultdict(int)
for b in buy: dd[b] += 1
if len(dd) == 1:
    for d in dd: print(d)
elif len(dd) == 2:
    for d in dd:
        if dd[d] == 1: print(d)
else:
    for i in range(4):
        if i in dd: continue
        else: print(i)