public class Stack<T> {
    private LinkedList<T> list;

    public Stack() {
        list = new LinkedList<>();
    }

    public Stack(T elem) {
        this();

    }

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

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

    public void push(T elem) {
        list.addFirst(elem);
    }

    public T pop() {
        return list.removeFirst();
    }

    public T peek() {
        return list.peekFirst();
    }

    public java.util.Iterator<T> iterator() {
        return list.iterator();
    }

    public String toString() {
        return list.toString();
    }
}