using System;

using System.Xml;

​

public static class Program

{

    public static void Main(string[] args)

    {

        var doc = new XmlDocument();

​

        doc.Load("http://video.cazin.net/rss.php");

​

        var nsManager = new XmlNamespaceManager(new NameTable());

​

        nsManager.AddNamespace("ab", "http://search.yahoo.com/mrss/");

​

        XmlNodeList xmlNode = doc.SelectNodes("rss/channel/item");

​

        var thumbnail = xmlNode[2].SelectSingleNode(".//ab:thumbnail/@url", nsManager);        

​

        Console.WriteLine(thumbnail.Value);

    }  

}