Crystal Reports Adding Quantity

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Hi, 
Hope someone can help me out for this.

This sounds so simple but yet I can't figure out how to add this.

Basically, I have two ITEM NOs and each one of it has LOT NUMBER.

ITEM                         LOT NUMBER             QUANTITY
0001                         101                           600
                                102                           400
1002                         103                           900

I want to sum up  the quantity of each ITEM and put the result in the quantity field. So in this case, the resul would be something like this.

ITEM                                                LOT NUMBER                         QUANTITY
0001                                                101                             1000
                                 102                            
1002                                                103                                                       900

I made a group for ITEM.. (ItemNum)    

I counted the LOT NUMBER using Running Field.. (TotalLotNum)
Field to summarize: Item.LotNum
Type of Summary: Distinct Count
Evaluate: Group 2 ItemNum
On each Field: Item.ItemNum

And then made a FORMULA FIELD and typed this formula in..

if (#TotalLotNum) > 1 then Quantity * 2

But this is giving me 0.00 result..

Can someone please help me out on this one. I spent too much time to solve this but still no luck.

Thanks so much...