import sys
input = lambda: sys.stdin.readline().rstrip()
from collections import Counter

##################

A = list(map(int, input().split()))
c = Counter(A)
if len(c) == 1:
  print(A[0])
elif len(c) == 2:
  if c[0] == 1:
    print(0)
  elif c[1] == 1:
    print(1)
  elif c[2] == 1:
    print(2)
  else:
    print(3)
else:
  print(list({0,1,2,3}-set(A))[0])