import java.util.*;
import java.util.concurrent.Semaphore;
public class DX{
	Semaphore mutex; //count
	Semaphore db; // w
	int count;

	public DX(){
		mutex = new Semaphore(1);
		db = new Semaphore(1);
		count = 0;
	}

	public void write(){
		db.acquire();
		System.out.println("Writer is working....");
		db.release();
	}

	public void read(){
		mutex.acquire();
		if (count == 0){
			db.acquire();
		}
		count++;
		mutex.release();
		System.out.println("Reader is working....");
		mutex.acquire();
		count--;
		if (count == 0){
			db.release();
		}
		mutex.release();
	}
	public static void main(String[] args){
		DX dx = new DX();

		Reader reader = new Reader(dx);
		Writer writer = new Writer(dx);

		reader.run();
		writer.run();
	}
}

public class Reader extends Thread{
	DX dx;
	public Reader(DX dx){
		super();
		this.dx = dx;
	}
	public void run(){
		while(true){
			dx.read();
			Thread.sleep(100);
		}
	}
}

public class Writer extends Thread{
	DX dx;
	public Writer(DX dx){
		super();
		this.dx = dx;
	}
	public void run(){
		while(true){
			dx.write();
			Thread.sleep(1000);
		}
	}
}