I need an answer fast.

1. (05-09-2022) There are n lockers in a hallway, numbered sequentially from 1 to n. Initially, all the locker doors are closed. You make n passes by the lockers, each time starting with locker \#1. On the i th pass, i=1,2,,n, you toggle the door of every i th locker: if the door is closed, you open it; if it is open, you close it. Thus, after the first pass every door is open; on the second pass, you only toggle the even-numbered lockers (#2,#4, ... ) so that after the second pass the even doors are closed and the odd ones are open; the third time through you close the door of locker \#3 (opened from the first pass), open the door of locker \#6 (closed from the second pass), and so on. After the last pass, how many of them are open