N = 0

N = 5

N = 10

N = 30

N = 45

N = 60

N = 90

Amazon

4

6

10

14

15

16

17

iTunes

3

5

9

14

14

15

16

Amazon or iTunes

5

7

11

16

17

19

20

Amazon and iTunes

2

4

8

12

12

12

13