Logout when use Form Authentication ASP.Net C# VB

 if (Request["Logout"] == "1")
        {
            ltrErrorMsg.Text = "You are successfully logged out !";
            Session.Contents.Clear();
            Session.Abandon();
            FormsAuthentication.SignOut();
            HttpCookie cookie = HttpContext.Current.Request.Cookies["Admin"];
            if (cookie != null)
            {
                Request.Cookies["Admin"].Expires = DateTime.Now.AddHours(-1);
                Response.Cookies.Add(cookie);
            }
        }