protected function crossSum($int)
    {
        $sum     = 0;
        $str_int = (string) $int;
        for ($i = 0; $i < strlen($str_int); $i++) {
            //$sum = bcadd($str_int{$i}, $sum);
            $sum += $str_int{$i};

        }
        return $sum;
    }