get value from dynmically added textbox in asp.net using master page

hi i am in great trouble .. my problem is that i can easily added control  in master page but i can't get velue from it . i use this code

        int n = int.Parse(TextBox1.Text);
            ContentPlaceHolder cph = (ContentPlaceHolder)this.Master.FindControl("MainContent");
            Panel p = (Panel)cph.FindControl("Panel1");
            Label1.Text="";
            try
            {
                for (int i = 1; i <= n; i++)
                {


            ...