How to check from a number of items in an entity's GUI

Hey there!

So I've been trying to create a mob which you can trade with, everything is working flawlessly, from the actual trading to the GUI. With only one exception; You see, one of the trades take 5 items instead of 1 to get a set number of items in return. This is working, at least the part where you get the set number of items in return. What is not working is checking for the number of items you need to trade with. (Basically, I want the trade to be 5 Copper coins to 15 Lepron (a new stone type))

For some reason this isn't exactly working, I tried adding the itemstack procedures, but they add a new dependency which the GUI trade button (which you click to get the traded item) won't accept. This is my procedure:

Am I doing something wrong here?

Thank you