public function min($input, $key, $min, $lang)
    {
        $lang = $this->custom('min', $lang);
        if (strlen($input[$key]) < $min) {
            return preg_replace_callback('/(:field)(.*)(\:num)/i',
            function ($m) use ($key, $min) {
                return $key.$m[2].$min;
            }, $lang);
        }
    }