EXPORT to memory..

i want to export the vlaue to memory before the selection screen is displayed:

DATA : lv_obtyp TYPE jsto-obtyp.

lv_obtyp = 'QMI'.

EXPORT lv_obtyp TO MEMORY ID 'PM_OBTYP'.

wher can i put this piece of code so tat the value is in memory before the selection screen is displayed

thanks