import java.util.*;

public class OurStack3 {

    // Use a linked list instead of an array.
    LinkedList<Character> list;


    public OurStack3 ()
    {
	// Can be unlimited in size now.
	list = new LinkedList<Character>();
    }


    public void push (char ch)
    {
        // No need to check for upper limit.
	list.add (ch);
    }


    public char pop ()
    {
	if (! list.isEmpty()) {
	    return list.removeLast();
	}
	else {
	    System.out.println ("ERROR in OurStack.pop(): stack empty");
	    return '@';
	}
    }


    public boolean isEmpty ()
    {
	return list.isEmpty();
    }

}