Exam - 17 September 2017 - 06. The song of the wheels

<?php
$n = intval(readline());
$counter = 0;
$password = "";
for($digit1 = 1; $digit1 <= 9; $digit1++){
    for($digit2 = 1; $digit2 <= 9; $digit2++){
        for($digit3 = 1; $digit3 <= 9; $digit3++){
            for($digit4 = 1; $digit4 <= 9; $digit4++){
                if ($digit1 < $digit2 && $digit3 > $digit4 && $digit1 * $digit2 + $digit3 * $digit4 == $n){
                    echo $digit1.$digit2.$digit3.$digit4." ";
                    $counter++;
                    if($counter == 4){
                        $password .= $digit1.$digit2.$digit3.$digit4;
                    }

                }
            }

        }
    }
}
if ($counter < 4)
{
    echo "\nNo!";
}
if ($counter >= 4)
{
    echo "\nPassword: ", $password;
}