13. Find the number of students

Among the class of 35 students, every student plays at least one of the given sports: cricket, volley ball and football. To be precise, 30 of them play cricket, 25 of them play volley ball, 20 of them play football, 18 of them play cricket and football, 16 of them play volley ball and football, and 5 play all the three sports. Find the number of students who play cricket and volley ball but not football.

 

Number of students who play cricket and volley ball but not football $=$ .