private static function convertToNumber(string $number): string
    {
        \preg_match_all('/(\D+)/', $number, $matches);

        if (\count(\array_unique($matches[0])) > 1) {
            throw new InvalidArgumentException(
                "The number '{$number}' seems to have decimal part. Only integer numbers are supported."
            );
        }

        return \preg_replace('/\D+/', '', $number);
    }