protected function convertNegativeTo($input)
    {
        $res = $this->convertPositiveTo(substr($input, 1));

        $res = strtr($res, static::POSITIVE_CHARS, static::NEGATIVE_CHARS);

        if (strlen($res) < 5) {
            $res = '/' . $res;
        } elseif ($res[0] !== '!') {
            $res = '*' . $res;
        }

        return $res;
    }