2025-12-27 16:45:10 +0300 MSK

class LUPrefix:
    def __init__(self, n: int):
        self._start = {}
        self._end = {}

    def upload(self, video: int) -> None:
        if video - 1 not in self._end and video + 1 not in self._start:
            self._start[video] = video
            self._end[video] = video
        elif video - 1 in self._end and video + 1 in self._start:
            end = self._start.pop(video + 1)
            start = self._end.pop(video - 1)
            self._start[start] = end
            self._end[end] = start
        elif video -1 in self._end:
            start = self._end.pop(video - 1)
            self._start[start] = video
            self._end[video] = start
        elif video + 1 in self._start:
            end = self._start.pop(video + 1)
            self._start[video] = end
            self._end[end] = video

    def longest(self) -> int:
        return self._start.get(1, 0)

# Your LUPrefix object will be instantiated and called as such:
# obj = LUPrefix(n)
# obj.upload(video)
# param_2 = obj.longest()