def main():

  seikai_list = [i for i in range(1, 11)]
  nyuryoku = list(map(int, input().split()))
  for i in nyuryoku:
    for s in seikai_list:
      if i == s:
        seikai_list.remove(s)
      else:
        continue
  print(seikai_list[0])

if __name__ == '__main__':
  main()