/* La classe Semaphore. */

public class Semaphore {
  private int value;

  public Semaphore(int n) {
    value = n;
  }

  public synchronized void P() {
    while (value <= 0) {
      try { wait(); } catch (InterruptedException e) {};
    };
    value--;
  }

  public synchronized void V() {
    value++;
    notifyAll();
  }
}