#include <iostream>
#include <future>
#include <mutex>
#include <thread>

class CycleBarrier {
    bool is_outing;
    int entered;
    int N;
    std::mutex m;
    std::condition_variable cv_outing;
    std::condition_variable cv_waiting;

public:
    CycleBarrier(int N) : N(N),is_outing(false),entered(0) {}

    void attendi(){
        std::unique_lock<std::mutex> l(m);

        while (is_outing) {
            cv_outing.wait(l);
        }

        entered++;

        if (entered == N){
            is_outing=true;
            cv_waiting.notify_all();
        } else {
            cv_waiting.wait(l,[this]{
                return is_outing;
            });

            entered--;

            if (entered==0)
                cv_outing.notify_all();
        }

    }


};