Unable to access a web Service using Asp .Net.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Services;

/// <summary>
/// Summary description for ws
/// </summary>
[WebService(Namespace = "http://tempuri.org/")]
[WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]
// To allow this Web Service to be called from script, using ASP.NET AJAX, uncomment the following line. 
// [System.Web.Script.Services.ScriptService]
public class ws : System.Web.Services.WebService {

    public ws () {

        //Uncomment the following line if using designed components 
        //InitializeComponent(); 
    }

    [WebMethod]
    public string HelloWorld() {
        return "Hello World";
    }
    
}

 protected void Page_Load(object sender, EventArgs e)
    {
        helloworldws.ws obj = new helloworldws.ws();
        string result = obj.HelloWorld();
        Response.Write(result);
    

    }