How to get Opening Balance for Stock Report in Crystal Report?

Dear Experts,

I am using SAP B1 8.82.

I am new to crystal report and now trying to do a monthly stock report with the following format:

Species  BatchNum   OpeningBal   QtyInKD    QtyInRD    QtyInCD   Adj    ClosingBal

ABC       T1234          17.43           10.16         17.43        0.00         0.00   10.16

ClosingBal = OpeningBal + QtyInKD - QtyInRD - QtyInCD + Adj

Parameters:

- DateFrom

- DateTo

- WarehouseFrom

- WarehouseTo

I am having problem in defining formula to get the opening balance for each item. The report is grouped by species, whscode & batchNum.

Anyone please share with me how to write the formula for opening balance in stock report.

Thanks.

Best Regards,

Leng