i need to find out which is cheaper, french fries in bags in groceries or

just buy my own potatoes and make my own french fries or just buy in the McDonalds. I do love eating french. Although i am avoiding eating hamburgers for now. i don't think it is bad to eat french fries . although it is not that healthy either because of fat anyway, the raw potato is not cheap either so. i will try to compute how much i can make in a half kilo of potato and half kilo in bags in groceries. and how much it would cost me. and how much i would save if i buy that instead in mcdonalds.