import java.util.ArrayList;
import java.util.List;

public class ProductStack {

    private List<Object> list = new ArrayList<Object>();
    private int currentIndex = -1;

    public void push(Object object) {
        list.add(object);
        currentIndex++;
    }

    public Object pop(){
        Object object = list.remove(currentIndex);
        currentIndex--;
        return object;
    }

    public int count() {
        return list.size();
    }

    public Object peek(){
        return list.get(currentIndex);
    }

    public void clear(){
        list.clear();
        currentIndex = -1;
    }
}