I'm trying to reduce the cell value in the column by 1 with duplicate and if condition

I'm working on an inventory replenishment tool. If column E says PICK and the barcode in Column A is Duplicate then the cell value (Warehouse stock) should reduce by 1 from Column C, else the same WH stock value in Column C. Please find the attached Screen shot:

Formula i tried, IF(E3="PICK",IF(COUNTIF($A$3:$A$9,$A3)>1,C3-ROW(A1),C3))