using System;

public class Program

{

    public static void Main()

    {

        Console.WriteLine($" 3 to Roman: {GetRomanNumber(3)}");

        Console.WriteLine($" 12 to Roman: {GetRomanNumber(12)}");

        Console.WriteLine($" 45 to Roman: {GetRomanNumber(45)}");

        Console.WriteLine($" 50 to Roman: {GetRomanNumber(50)}");

    }

​

    private static string GetRomanNumber(int decimalNumber)

    {

        if (decimalNumber == 0)

            return string.Empty;

​

        if (decimalNumber < 0)

            throw new ArgumentOutOfRangeException("Decimal must be positive number");

​

        if (decimalNumber > 50)

            throw new ArgumentOutOfRangeException("Decimal must be less than 50");

​

        var sb = new System.Text.StringBuilder();

        string[] romanUnits = new string[] { "I", "II", "III", "IV", "V", "VI", "VII", "VIII", "IX" };

        string[] romanTens = new string[] { " ", "X", "XX", "XXX", "XL", "L" };

​

        if (decimalNumber > 9)

        {

            int tens = decimalNumber / 10;

            int units = decimalNumber % 10;

            sb.Append(romanTens[tens]);

            decimalNumber = units;

        }

​

        if (decimalNumber > 0)

            sb.Append(romanUnits[decimalNumber - 1]);

​

        return sb.ToString();

​

    }

}