import java.awt.*;

class Stock extends IntLabel{
private static final int max=30;

	Stock(Label lb){ super(lb); }

	boolean full(){ return get()>=max; }

	boolean empty(){ return get()<=0; }

	synchronized void buy(){
		while(empty()){
			try{ wait(); }catch(Exception e){}
		}
		super.dec();
		notifyAll();
	}

	synchronized void supply(){
		while(full()){
			try{ wait(); }catch(Exception e){}
		}
		super.inc();
		notifyAll();
	}

}