<?php
fscanf(STDIN,"%s",$a);
fscanf(STDIN,"%s",$b);
fscanf(STDIN,"%s",$c);
$ary=[$a,$b,$c];

if($a===$b || $a===$c) echo $a . PHP_EOL;
if($a!==$b && $b===$c) echo $b . PHP_EOL;