class H2O {
    //controls between different h2o
    private final Object lock = new Object();
    private volatile AtomicInteger hy_count = new AtomicInteger(0);
    private volatile AtomicInteger ox_count = new AtomicInteger(0);
    //controls inside a h2o
    private Semaphore hy_2entry = new Semaphore(2);
    private Semaphore ox_1entry = new Semaphore(1);

    public H2O() {
    }

    public void hydrogen(Runnable releaseHydrogen) throws InterruptedException {
		hy_2entry.acquire();

        //work stuff
        releaseHydrogen.run();
        hy_count.incrementAndGet();

        if(hy_count.get()>1){
            synchronized(lock){  
                while(ox_count.get()<1)
                    lock.wait();
				ox_count.getAndAdd(-1);
				hy_2entry.release(2);
				lock.notifyAll();
            }
        }
    }

    public void oxygen(Runnable releaseOxygen) throws InterruptedException {
        ox_1entry.acquire();
        
        //work stuff
		releaseOxygen.run();
        ox_count.incrementAndGet();

        if(ox_count.get()>0){
            synchronized(lock){
                while(hy_count.get()<2)
                    lock.wait();
				hy_count.getAndAdd(-2);
				ox_1entry.release();
				lock.notifyAll();
            }
        }
    }
}