Bex Cumulative Key Fig

We have 2 key fig like A & B in Bex .

A – normal key fig

B –  checked cumulative in Bex key fig properties -> Calculation – check cumulative.

my requirement is display Key fig A, B & C.

where C = A + B,  C – formula

Retort output coming is below which is wrong bcause B value is cube level value( original value ) not report level value

when we adding A + B in C column the output is coming key fig original value not Cumulative value. Means

Cube level Data is adding & displaying report.  I need the Cumulative value which will be adding with A .

Kindly suggest me.. if it is possible..

Regards,

Kamruz