text: '''
  1、位运算
  '''
  
  from typing import List
  
  
  class Solution:
      def single_number(self, nums: List[int]) -> int:
          if len(nums) <= 0:
              raise Exception("nums is invalid!")
  
          res = 0
          for i in nums:
              res ^= i
  
          return res
  
  
  if __name__ == '__main__':
      nums = list(map(int, input().split()))
      s = Solution()
      res = s.single_number(nums)
      print(res)
  