Even rooms

In a big hostel there are 1000rooms the rooms are numbered in even numbers only. All the rooms have a resident each. One day the warden called all the residents and tell them to go back to their rooms as well as multiples of their room number. When a guy visited his room he found the gate open, he closes it and if door is closed, he opens it, all 1000guys do this operation . All doors were open initially

The last room that is closed is which room number