Display sum of Column total in ASP.Net GridView Footer using C# and VB.Net

grid view column sum but not finding the total sum in footer

not finding sum last line please help me?

            if (e.Row.RowType == DataControlRowType.DataRow)
            {
                decimal netpremium = Convert.ToDecimal(e.Row.Cells[2].Text);
                decimal vat = Convert.ToDecimal(e.Row.Cells[3].Text);
                decimal registry = Convert.ToDecimal(e.Row.Cells[4].Text);
                Label lblTOTAL = (Label)e.Row.Cells[6].FindControl("lblTOTAL");

                decimal sum = netpremium + vat + registry;
                lblTOTAL.Text += sum.ToString();                
            }
            else if(e.Row.RowType==DataControlRowType.Footer)            
            {
                //e.Row.Cells[6].Text = string.Format("{0:c}", sum);
                //GridView1.FooterRow.Cells[4].Text = dt.Compute("Sum(BANK_RECEIVED)", "").ToString();
                //Label lbl = (Label)e.Row.FindControl("lblTotal");
                //lbl.Text = sum.ToString();
                //lbl.Text = "Total Value is : " + sum.ToString();
                (e.Row.FindControl("Total") as Label).Text = sum.ToString();
            }