using System;

using System.Text.RegularExpressions;

public class Program

{

    public static void Main()

    {

        string formatted;

        MssFormatTMInternationalNumber("12312321321ae", out formatted);

        Console.WriteLine(formatted);

    }

    public static void MssFormatTMInternationalNumber(string ssInternationalNumber, out string ssFormattedNumber) {

    ssFormattedNumber = "";

​

    ssInternationalNumber = ssInternationalNumber.Trim();

    if (string.IsNullOrEmpty(ssInternationalNumber)) return;

​

    var pattern = new Regex("^([0-9]+)([a-z]+)?$", RegexOptions.IgnoreCase);

    var match = pattern.Match(ssInternationalNumber);

​

        Console.WriteLine(match.Groups[0].Value);

    if (!match.Success || match.Groups.Count < 2)

    {

        ssFormattedNumber = "MD/M/"+ssInternationalNumber;

        return;

    }

​

    if (match.Groups.Count > 2)

    {

        ssFormattedNumber = match.Groups[2].Value;

    }

    else

    {

        ssFormattedNumber = "MD";

    }

​

    ssFormattedNumber += "/M/" + match.Groups[1].Value;

​

} 

}