using System;

using System.Collections.Generic;

using System.ComponentModel;

using System.Data;

using System.Drawing;

using System.Linq;

using System.Text;

using System.Threading.Tasks;

using System.Windows.Forms;

using System.Xml.Linq;

using System.Xml;

using HtmlAgilityPack;

public class Program

{

    public static void Main()

    {

                    var html = @"<TD class=texte width=""50%"">

<DIV align=right>Name :<B> </B></DIV></TD>

<TD width=""50%"">

    <INPUT class=box value=John maxLength=16 size=16 name=user_name>

</TD>

<TR vAlign=center>";

​

            var htmlDoc = new HtmlDocument();

            htmlDoc.LoadHtml(html);

​

            string name = htmlDoc.DocumentNode

    .SelectNodes("//td/input")

    .First()

    .Attributes["value"].Value;

        Console.WriteLine(name);

    }

}