Coffee Club Card

So, my campus coffee shop has a card. When you buy a coffee, you get a punch. After ten punches, you get a free coffee. So, at the outset when you are about to buy that first coffee, you have a funny supply curve that you face. The price line is at the price of coffee for the first ten, but then it goes down to zero for the eleventh, then the price for the next ten, and so on. This isn't very interesting... just something I was thinking about as I drank my coffee today.