Total Books Read Over a Month

A class of students kept track of how many books they read over a month. They created a bar graph to show their progress. The graph indicates the number of books read each week.

In week 1, they read 3 books. In week 2, they read 5 books. In week 3, they read 2 books, and in week 4, they read 4 books.

How many total books did the students read at the end of the month?