some error in code of report

i have shipment report with return order in report :
this is shipment report with return order(all values in table sales shippment line table) as following:
doc no order no quantity
12 15 50
12 15 50-
11 20 30
19 21 50
20 32 25
20 32 -25
WHAT I NEED IS :
1-i want to show shipment report without return order as following:
doc no order no quantity
11 20 30
19 21 50
20 32 25
meaning i don't want any document no returned because returned order must be negative value to cancelled order that make by wrong so that i don't want to display returned in report.
this report based on sales shipment header and sales shipment line table how i write code to make this result .
i write this code on pre section on report to solve the problem but i not reached the result
Sales Shipment Header, Body (1) - OnPreSection()

SalesShipmentLine.Set Range("Document No.","No.");
SalesShipmentLine.Set Filter(Quantity,'<%1',0);
If SalesShipmentLine.Find First then
If Not Show Neg then
Curr Report.SHOW OUTPUT(False);
Else
If Show Neg then
Curr Report.SHOW OUTPUT(False);
this logic i want to write code with it
1-search for positive quantity
2- if you found similar document number with negative value then select it
please help me
thanks