In these quarantine days, a list of what Max may do on a typical day is given in a table with the starting hour to ending hour.

 Task       Start         End
Sleep         0            6
Walk          6            7
Breakfast     8            9
Movie         10           16
Study         15           21
Dinner        22           23

Now Max wants to perform the maximum amount of tasks in a single day. How should he make his routine?

For this problem -- just return the number of tasks.