need logic for this output itab format

hi guys

i need the output itab in following format

i have data in my present itab

itab-f1 itab-f2 itab-f3

AAA 10 (means null,' ')

AAA 20

BBB 10

BBB 20 A1

BBB 30

and i want output in following way output itab

itab-f1 itab-f2 itab-f3

AAA 30

BBB 60 A1

can anyone suggest me code for this