A man walked into a hardware store. He saw the items he was looking for, but there were no prices on the items. He walked up to a store employee and asked, "How much are those?" The employee said, "They are a dollar apiece." "You mean I could get 10 for two dollars?", said the customer. "That's right," said the employee. "Well," said the customer, "I need 200." And the employee replied, "OK. That will cost you three dollars." If you know what the customer is buying, the conversation makes perfect sense. What is he buying?