Unlock these lockers

There are 1000 lockers (initialy all are closed) and 1000 students in a school. Teacher ask the 1st student to go to each locker and open it , then the teacher ask 2nd student to go to every 2nd locker and close it , 3rd student to go to every 3rd locker if close then open or open then close it and the same goes on till 1000th student.

How many lockers are closed at last?

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