using System;

using System.Text.RegularExpressions;

​

public class Program

{

    public static void Main()

    {

        const string shortagePattern = @"^([^\.]+)(?:\.)?(\d+)?$";

        Regex shortageRegex = new Regex(shortagePattern, RegexOptions.Compiled);

        var match = shortageRegex.Match("urn:GangNbr:787333179");

        if (match.Success)

        {

            var shortCount = 0;

            if (match.Groups.Count == 3)

            {

                int.TryParse(match.Groups[2].Value, out shortCount);

            }

​

            shortCount++;

            Console.WriteLine(match.Groups[1].Value + "." + shortCount);

        } else {

            Console.WriteLine("No match");

        }

    }

}