#include <iostream>
#include <vector>
#include <queue>

using namespace std;

const int WINDOW_SIZE = 5; // size of the sliding window

class SlidingWindow {
private:
    vector<int> sent_frames; // queue of sent frames
    int next_frame_to_send; // index of the next frame to send
    int next_frame_to_receive; // index of the next frame to receive

public:
    SlidingWindow() : next_frame_to_send(0), next_frame_to_receive(0) {}

    // send a frame
    void send_frame(int frame_number) {
        if (sent_frames.size() < WINDOW_SIZE) {
            sent_frames.push_back(frame_number);
            next_frame_to_send++;
            cout << "Sent frame " << frame_number << endl;
        } else {
            cout << "Window is full, cannot send frame " << frame_number << endl;
        }
    }

    // receive a frame
    void receive_frame(int frame_number) {
        if (frame_number == next_frame_to_receive) {
            next_frame_to_receive++;
            cout << "Received frame " << frame_number << endl;
        } else {
            cout << "Received frame " << frame_number << ", but expected frame " << next_frame_to_receive << endl;
        }

        // remove acknowledged frames from the sent_frames queue
        while (!sent_frames.empty() && sent_frames.front() <= next_frame_to_receive - 1) {
            sent_frames.erase(sent_frames.begin());
        }
    }
};

int main() {
    SlidingWindow window;

    // send some frames
    window.send_frame(0);
    window.send_frame(1);
    window.send_frame(2);
    window.send_frame(3);
    window.send_frame(4);
    window.send_frame(5);

    // receive some frames
    window.receive_frame(0);
    window.receive_frame(1);
    window.receive_frame(2);
    window.receive_frame(3);
    window.receive_frame(4);

    return 0;
}