Regarding :to sum the field value of a segment

I have on requirement. in tht based on the condition . i have to sum the quantity field of one segment.

here e1edp01 is a segment which stores item level values.

in e1edp01 there is one field menge.

if my condition satisfies

i have to sum all the e1edp01-menge values for the given material.

e1edp01 is also having matnr.so for one matnr i have more than one quantites.

so PLz tell me how to sum the menge field values in tht segment

thanks in advance

pavan