A survey of 50 math students on the following question "what did you think about during your math lectures?" yielded the following information:

all but 5 had thought about partying,food,sports
10 had thought of partying,food, and sports
30 had thought about partying
35 had thought about food
22 had thought about sports
13 had thought about food and partying, but not sports
5 had thought of only food

Using a venn diagram, how many thought only of partying?