public function numberToRomanNumerals(int $number): string
    {
        if ($number < 1) {
            // Cannot convert zero/negative numbers
            return (string) $number;
        }
        $roman = '';
        foreach (self::ROMAN_NUMERALS as $key => $value) {
            while ($number >= $key) {
                $roman  .= $value;
                $number -= $key;
            }
        }

        return $roman;
    }