How many books in the Heroes of Olympus series?
6
3
3
3
3
5
3
4
5
3
4
5
3
4
2
5
3
4
2
5
3
4
2
5
3
4
2
5
3
4
2
5
3
4
2
5
3
4
2
5
3
4
2
5
1
6
3
4
2
5
7
1
6
3
4
2
5
7
1
6
3
4
2
5
7
1
6
3
4
2
5
7
1
6
3
4
2
5
7
1
6
3
4
2
5
7
1
6
4
2
5
7
1
6
4
8
2
5
7
1
6
4
8
2
5
7
1
6
4
8
2
7
1
6
8
2
7
1
6
8
2
7
9
1
6
8
7
9
1
10
6
8
7
9
11
1
10
6
8
7
9
11
1
10
6
8
7
9
11
1
12
10
13
6
8
7
9
11
1
12
10
13
6
8
7
9
11
1
12
10
13
6
8
7
9
11
1
12
10
13
6
8
7
9
11
12
10
13
8
9
11
12
10
13
8
9
4 books
3 books
5 books
2 books
7 books