using System;

public class Program

{

    public static void Main()

    {

        //Your input url

        Uri inputurl = new Uri("http://www.xyz.com/forums/AddPost/NewPost/Hello");

        //Get the domain part of url

        string requested = inputurl.Scheme + Uri.SchemeDelimiter + inputurl.Host;

        //Create a URI from it

        System.UriBuilder uriBuilder = new System.UriBuilder(requested);

        //Replace the lAST THREE slash with comma

        uriBuilder.Path += inputurl.PathAndQuery.Replace("/", ",").TrimStart(',');

        //ouput the result

        Uri url = uriBuilder.Uri;

        Console.WriteLine(url);

    }

}