In the funny elementary school cafeteria, lunch for 100 people is served. but it is topsy turvey, and the waiters are acting funny. the first waiter turned every plate upside down. then another waiter turned every other plate. then the third waiter turned every third plate (so if a plate was upside down it was placed normally, but if it was placed normally, it became upside down). the fourth waiter turned every fourth plate, and so on, until the hundredth waiter turned the hundredth plate. at the end, how many plates were placed normally?