using System;

using System.Web;

using System.Net;

public class Program

{

    public static void Main()

    {

        var url = "https://www.youtube.com/watch?v=NHfWY0is3rE";

        string name = GetTitle(url);

        Console.WriteLine(name);

    }

    public static string GetTitle(string url) =>

        GetArgs(new WebClient().DownloadString($"http://youtube.com/get_video_info?video_id={GetArgs(url, "v", '?')}"), "title", '&');

​

    private static string GetArgs(string args, string key, char query)

    {

        var iqs = args.IndexOf(query);

        return iqs == -1

            ? string.Empty

            : HttpUtility.ParseQueryString(iqs < args.Length - 1 ? args.Substring(iqs + 1) : string.Empty)[key];

    }

}