<?php
fscanf(STDIN, "%d %d", $b, $c);

$tmp_b = $b;
$tmp_c = $c;
if (preg_match("/4|7/", $b) && preg_match("/4|7/", $c) && checkdata($b,$c)){
    $list = array("4"=>"7", "7"=>"4");
    $tmp_b = strtr($b, $list);
    $tmp_c = strtr($c, $list);
}


if($tmp_b < $tmp_c) echo $c;
if($tmp_c < $tmp_b) echo $b;

echo "\n";


function checkdata($b,$c){
    if(strstr($b,"4") && strstr($c,"4")){
        if(!strstr($b,"7") && !strstr($c,"7")) return false;
    }
    if(strstr($b,"7") && strstr($c,"7")){
        if(!strstr($b,"4") && !strstr($c,"4")) return false;
    }
    return true;
}
?>