public class SemProducerConsumer {
    private int N, buf[], nxtC, nxtR;
    private Semaphore cSem, rSem;

    public SemProducerConsumer (int N) {
        this.N = N;
        buf = new int[N];
        nxtC = 0;
        nxtR = 0;
        cSem = new Semaphore(N);
        rSem = new Semaphore(0);
    }

    public void Insert (int i) {
        cSem.P();
        buf[nxtC] = i;
        nxtC = (nxtC + 1) % N;
        rSem.V();
    }

    public int Remove () {
        int i;
        rSem.P();
        i = buf[nxtR];
        nxtR = (nxtR + 1) % N;
        cSem.V();
        return i;
    }
}