How to get the value of a variable in group footer in the report footer also

I have a placed a formula as below at the group footer and the report footer. The data is grouped on the basis of duedays which is again formula and the value in that is appearing correctly.

Whilereadingrecords;

Global Numbervar CNTONE;

Numbervar P := P+1;

IF P = 1 AND {@DUEDAYS} = 0

THEN CNTONE := {spSUPPLIERSOA;1.INVOICEBAL}

ELSE IF P>1 AND {@DUEDAYS} = 0

THEN CNTONE := CNTONE + {spSUPPLIERSOA;1.INVOICEBAL}

At the group footer I get the value correctly for CNTONE but when I place the formula in Report footer I get the value for CNTONE as 0.

Please do let me know how I could get the same value in the report footer also.

Regards

Sreejith J