Start Routine to add missing month and values of those months

Hi

In the psa I have:

Material - Valuated Area - period - year - values - qty

X - 2400 - 01 - 2016 - 200 - 5

X -2400 - 02 - 2016 - 150 - 3

X-2400 - 04 - 2016 - 100 - 2

I want in start routine to add missing months then make qty = last value of previous month of missing month

like 03 will be 150 and 3

how to do this? please help