// Stack implementation with arrays

public class IntStack {
    private int capacity = 1000;
	private int [] items = new int [capacity];
	private int top = -1;
	
	public IntStack() {
		// do nothing	
	}
	
	public boolean isEmpty() {
		return top == -1;	
	}
	
	public int pop() throws StackException {
		if(!isEmpty()) {
			int n = items[top];
			top--;
			return n;			
		}
		else throw new StackException("Stack underflow");
	}
	
	public void push(int n) throws StackException {
		if (top == capacity - 1) 
		    throw new StackException("Stack overflow");
		top++;
		items[top]=n;
	}
}

public class StackException extends RuntimeException {
	public StackException(String s) {
		super(s);
	}
}