'use strict'

function main(s) {

  s = s.split('\n')[0].split(' ');
  let ans = '';
  
  if (s[0] !== s[1] && s[1] === s[2]) ans = s[0];
  if (s[0] !== s[1] && s[1] !== s[2]) ans = s[1];
  if (s[0] === s[1] && s[1] !== s[2]) ans = s[2];

  console.log(ans);
}

main(require("fs").readFileSync("/dev/stdin", "utf8"));
