Crystal Reports how summarize a formula field

Message

     Hi All

Iam desinging a report in which iam facing a problem to summarize the formula field . This formula field contains sum calculation like

formula name is @sales

Sum ({@DTM200}, {@SaleMan})+Sum ({@DTM500}, {@SaleMan})+

Sum ({@TM500}, {@SaleMan})+Sum ({@TM1000}, {@SaleMan})+

Sum ({@HTM500}, {@SaleMan})+Sum ({@HTM1000}, {@SaleMan})+

Sum ({@WM500}, {@SaleMan})+Sum ({@WM1000}, {@SaleMan})+

Sum ({@CURD}, {@SaleMan})+Sum ({@Buttermilk}, {@SaleMan})+

Sum ({@BULKWM}, {@SaleMan})+Sum ({@BULKTM}, {@SaleMan})

the fields are summary fields and iam calculating all these fields to get the final result . Upto this it is working fine but finally i want to calculate the grand total of this formula '@sales' how should do this  

Thanks in advance