Start routine/ABAP help

Hi Gurus,

I need help with Abap.

I am facing a problem during a flat file load. The format I get the file is as shown below .

Comp code    Account     Profit center    Fisc year    Jan       Feb       March... etc

001                100            1000                  2016          $100     $110     $120
002                 200           2000                  2016          $200     $210     $220

I want to convert it into to the following format using Start routine and also need to populate an Accumulated balance field

Comp code     Account     Profit Center     Fis year     posting period     Amount     Accum. Bal (calculate YTD based amount rollup)

001                   100          1000                    2016         001                    100               100

001                    100          1000                    2016         002                    110              210

001                    100          1000                    2016          003                    120              330

002                    200          2000                    2016          001                    200               200

002                    200          2000                    2016          002                    210               410

002                    200          2000                    2016           003                    220              630....etc

any help will be highly appreciated

Thanks,