How to capture textbox value into a file name when using ajax upload?

I am using this Ajax upload code. it is working fine however, I want to be able to add the value of the textbox to the file name before I save all files. I am not able to capture the value of the text box into the file name and save the file.

        <%@ Page Title="" Language="C#" MasterPageFile="~/Site.Master" AutoEventWireup="true" 
    CodeBehind="AjaxUpload.aspx.cs" Inherits="contactDirectory.demo.AjaxUpload" %>
    <%@ Register Assembly="AjaxControlToolkit" Namespace="AjaxControlToolkit" TagPrefix="asp" %>
    <asp:Content ID="Content1" ContentPlaceHolderID="MainContent" runat="server">
    <div align="center">
        <asp:TextBox ID="txtName" runat="server" AutoPostBack="False"></asp:TextBox>
        <asp:AjaxFileUpload ID="AjaxFileUpload1" runat="server"  
            AllowedFileTypes="jpg,jpeg,png,gif,doc,pdf,xls,docx,xlsx"
            MaximumNumberOfFiles="10" 
            OnUploadComplete="File_Upload" 
            onUploadCompleteAll="AjaxFileUpload1_UploadCompleteAll"
            onUploadedStart="AjaxFileUpload1_UploadStart"
            Width="500px" />
    </div>
    </asp:Content>

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using AjaxControlToolkit;

namespace contactDirectory.demo
{
    public partial class AjaxUpload : System.Web.UI.Page
    {
        string filename = "";
        protected void Page_Load(object sender, EventArgs e)
        {
        }
        protected void File_Upload(object sender, AjaxFileUploadEventArgs e)
        {
          filename = e.FileName + txtName.Text;
           string strDestPath = Server.MapPath("~/documents/" + filename);
           AjaxFileUpload1.SaveAs(strDestPath + filename);
        }
        protected void AjaxFileUpload1_UploadCompleteAll(object sender, AjaxFileUploadCompleteAllEventArgs e)
        {
        }
        protected void AjaxFileUpload1_UploadStart(object sender, AjaxFileUploadEventArgs e)
        {
        }
    }
}