Apply top & Group By

I want to show top selling items for each store. Sample SQL Query is "SELECT TOP n ItemNumber FROM Inventory Group By Store" n - is the dynamic value. I am accepting this n parameter from the user. If the user is giving 5 for n then, I want to show top 5 selling items for each store. It will be greatfull, If anybodies giving me an idea of how to do this?.

Thanks

I have done it with the row_number function.