private static function cleanUp(string $number) : string
    {
        $firstChar = $number[0];

        if ($firstChar === '+' || $firstChar === '-') {
            $number = \substr($number, 1);
        }

        $number = \ltrim($number, '0');

        if ($number === '') {
            return '0';
        }

        if ($firstChar === '-') {
            return '-' . $number;
        }

        return $number;
    }