ASP .NET2 : Calculate total in Gridview and show it in Footer

//write this coding in gridview_rowdatabound()

if (e.Row.RowType == DataControlRowType.DataRow)
{
ColumnTotal += Convert.ToDecimal(DataBinder.Eval(e.Row.DataItem, "Amount"));


}
else if (e.Row.RowType == DataControlRowType.Footer)
{
e.Row.Cells[6].Text = "Total Rs:";
e.Row.Cells[8].Text = ColumnTotal.ToString();


e.Row.Font.Bold = true;
}