How many Dark Tower series are there?
9
4
4
2
3
4
2
3
4
2
3
4
2
3
5
4
2
3
5
4
2
3
5
4
2
3
5
4
6
1
2
3
5
4
6
1
2
3
5
4
6
1
2
3
5
4
6
1
2
3
5
4
6
1
2
3
7
5
4
6
1
2
3
7
5
4
6
1
2
3
7
5
4
6
1
8
2
3
7
5
4
6
1
8
2
3
7
5
4
6
1
8
2
3
7
5
4
6
1
8
2
3
7
5
4
6
1
8
2
3
7
5
6
1
8
2
3
7
5
6
1
8
9
7
5
6
1
8
0
9
7
5
6
1
8
0
9
7
5
6
1
8
9
7
6
1
8
9
7
6
1
8
10
9
7
6
1
8
10
9
7
8
10
9
7
8
10
9
7
8
10
9
7
8
10
9
7
8
10
9
8
10
9
8
10
9
10
9
10
9
11
10
9
11
10
9
11
12
13
10
ten