public string GetSpelt(int input)
        {
            if (input < 0 || input >= 1000)
            {
                throw new ArgumentOutOfRangeException();
            }

            var spelt = _units.GetSpelt(input);

            if (!string.IsNullOrWhiteSpace(spelt))
            {
                return(spelt);
            }

            var hundreds  = input / 100 * 100;
            var remainder = input - hundreds;
            var tens      = remainder / 10 * 10;

            remainder -= tens;
            var singles = remainder % 10;
            var result  = new StringBuilder();

            AppenHundreds(result, hundreds);
            AppendAnd(result, hundreds, tens, singles);
            AppendTensAndSingles(result, tens, singles);

            return(result.ToString());
        }