There are 5 different dishes and 3 different staple foods in the school cafeteria. Each person can only buy one dish and one staple food. Among the 16 students, there must be at least two students who buy the same dishes and staple foods. ,Why?
学校食堂有5种不同的菜和3种不同的主食，每人只能买一种菜和一种主食，在16名同学中，一定至少有两名同学所买的菜和主食都是相同的，为什么？
<result>16</result>