import time
from collections import deque


class Server:
    def __init__(self, dt):
        self.dt = dt
        self.queue = deque()
        self.last_ids = set()
        self.all_ids = {}

    def register_event(self, id):
        self.queue.append((id, time.time()))
        self.all_ids[id] += 1
        if self.all_ids[id] > 1000:
            self.last_ids.add(id)

    def check(self, ntime):
        while len(self.queue):
            q = self.queue.popleft()
            if ntime - q[1] <= self.dt:
                self.queue.appendleft(q)
                break
            self.all_ids[q[0]] -= 1
            if self.all_ids[id] < 1000 and q[0] in self.last_ids:
                self.last_ids.remove(q[0])

    def get_ids(self):
        self.check(time.time())
        return self.last_ids