Locker Problem

LEFT: Decrease step. RIGHT: Increase step.
SPACE: FAST MOOODE.

The Locker Problem goes as follows:

1. 100 lockers, closed. There are 100 people.
2a. Person 1 opens all, every first locker.
2b. Person 2 closes every second locker.
2b. Person 3 changes the state of every third, and so on.
3. Changing state means if opened, close; if closed, open.
4. After 100 people, which are opened?

The highlighted lockers are the ones just updated.