Getting Group-by By Record Value In Second Row?

I have following query

Select Date, Item_Code, SUM(In_Quantity) as In_Quantity, SUM(Issue_Quantity) as Issue_Quantity, (SUM(In_Quantity)-SUM(issue_Quantity)) as BalanceQty from

(
select tbl_add_product.Date as Date, tbl_add_product.Item_Code, tbl_add_product.In_Quantity, 0 as Issue_Quantity from tbl_add_product
where Item_Code = 'pen'
union ALL
select tbl_issue_product.Date as Date, tbl_issue_product.Item_Code, 0 as In_Quantity, Issue_Quantity from tbl_issue_product
where Item_Code = 'pen'
)
X group by Item_Code, Date

which gives following result:

**Date Item_Code In_Quantity Issue_Quanitity BalanceQty**
2014-12-02 pen 100 0 100
2014-12-03 pen 50 50 0

I want to 100 in second row. the logic is that balance Qty from first row should be added to In_Qty so that when Issue_Quantity is subtracted from it, it gives BalanceQty