process.stdin.resume();
process.stdin.setEncoding('utf8');
 
// your code goes here
var readline = require('readline');
 
var rl = readline.createInterface({
  input: process.stdin,
  output: process.stdout,
  terminal: false
});
 
rl.on('line', function (line) {
  var arr = line.split('');
  for (var i = 0; i < arr.length; i++) {
    var count = 0;
    for (var j = 0; j < arr.length; j++) {
      if (arr[i] === arr[j]) {
        count++
      }
    }
    }
    if (count == 2) {
      let res = arr.join('')
      console.log(res)
    }
});
 

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YXNkZgpmZGFzCmFzZHMKZCBmbQpkZmFhCmFhYWE=

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