How to choose a desktop folder

namespace photoshops
{
    public partial class WebForm1 : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
        }
        protected void Button1_Click(object sender, EventArgs e)
        {
            onflbload(sender, e);
        }
        public void onflbload(object sender, EventArgs e)
        {
            string filename = Server.MapPath("~/photo") + FileUpload.PostedFile.FileName;
            FileUpload.PostedFile.SaveAs(filename);
            SqlConnection connection = new SqlConnection();
            connection.ConnectionString =@"Data Source=DEVI\SQLEXPRESS; Initial Catalog =cat; Integrated Security=SSPI";
               
            try
            {
                connection.Open();
                SqlCommand cmd = new SqlCommand("insert into tblphotosettings "
                 + "(BillNo,CustomerName,Address,StartDate,EndDate,Systemurl,Numberofcopies,Amount,Total ) values (@BillNo,@CustomerName,@Address,@StartDate,@EndDate,@Systemurl,@Numberofcopies,@Amount,@Total)", connection);
                cmd.Parameters.Add("@BillNo", SqlDbType.NVarChar).Value = TextBox1.Text;
                cmd.Parameters.Add("@CustomerName", SqlDbType.NVarChar).Value = TextBox2.Text;
                cmd.Parameters.Add("@Address", SqlDbType.NVarChar).Value = TextBox3.Text;
                cmd.Parameters.Add("@StartDate", SqlDbType.NVarChar).Value = Rdbsdate.SelectedDate;
                cmd.Parameters.Add("@EndDate", SqlDbType.NVarChar).Value = Rdbddate.SelectedDate;
                cmd.Parameters.Add("@Systemurl", SqlDbType.VarChar).Value = filename;
                cmd.Parameters.Add("@Numberofcopies", SqlDbType.NVarChar).Value = TextBox7.Text;
                cmd.Parameters.Add("@Amount", SqlDbType.NVarChar).Value = TextBox8.Text;
                cmd.Parameters.Add("@Total", SqlDbType.NVarChar).Value = TextBox9.Text;
                cmd.ExecuteNonQuery();
            }
            
            finally
            {
                connection.Close();
            }
        }
    }
}