public class Semaphore
{
    private int value;

    public Semaphore(int init)
    {
        if(init < 0)
            init = 0;
        value = init;
    }

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

    public synchronized void v()
    {
        value++;
        notify();
    }
}