100 closed locks Puzzle

Suppose you are in hallway lined with 100 closed lockers.

You begin by opening every locker. Then you close every second locker. Then u go to every third locker and open it (if it's closed) or close it (if it's open). Lets call this action toggling a locker. Continue toggling every nth locker on pass number n. After 100 passes, where you toggle only locker #100, How many lockers are open???

Watch this space for answer in a week.