How many of the Heroes of Olympus books are there?
5
3
3
3
3
2
4
3
5
2
4
3
5
1
2
4
3
5
1
2
4
3
5
1
2
4
3
5
1
2
4
3
5
1
2
4
3
5
1
2
4
3
5
1
2
4
3
5
1
2
4
3
5
1
2
4
3
6
5
1
2
4
3
6
5
1
7
2
4
3
6
5
1
7
2
4
3
6
5
1
7
2
4
3
6
5
1
7
2
4
3
6
5
1
7
2
4
6
5
1
7
2
4
6
5
1
7
2
4
6
5
1
7
2
4
6
5
8
1
7
6
8
1
7
6
8
7
6
8
7
9
6
8
7
9
6
8
7
9
10
6
8
7
9
10
6
8
7
9
13
10
6
11
8
7
9
13
10
12
6
11
8
7
9
13
10
12
6
11
8
7
9
13
10
12
11
8
7
9
13
10
12
11
8
9
13
10
12
11
8
9
13
10
12
11
128
4 books
128
4 books
128
2 books