How To get screen value(lifnr) of fb01 or fb60 in the badi

i have a modfication in ehich i have to display a message based on the bseg-lifnr value in transaction fb60 and fb01

fb60: INVFO-ACCNT

fb01: RF05A-NEWKO

both get mapped in the work area bseg-lifnr.....

ZFI_TRANS_DATE_DERIV is the implementation of the badi FI_TRANS_DATE_DERIVE

how do i get the value of bseg-lifnr or individuallly the values as mentioned above??

plz help me

thanx