public class DoublyLinkedList<E> {

    private static class Node<F> {
        F val;
        Node<F> prev, next;

        public Node(F v, Node<F> p, Node<F> n) {
            val = v;
            p = prev;
            next = n;
        }
    }

    Node<E> first, last;
    int size;

    public DoublyLinkedList() {
        first = null;
        last = null;
        size = 0;
    }

    /**
     * Returns the number of items in the list.
     * @return the number of items in the list.
     */
    public int size(){
        return size;
    }

    /**
     * Returns the first item in the list.
     * 
     * @return the first item in the list.
     */
    public E getFirst() {
        // TODO
        return null;
    }

    /**
     * Returns the last item in the list.
     * 
     * @return the last item in the list.
     */
    public E getLast() {
        // TODO
        return null;
    }

    /**
     * Adds the given item to the start of the list.
     * 
     * @param item the item to be added.
     */
    public void addFirst(E item) {
        // TODO
    }

    /**
     * Adds the given item to the end of the list.
     * 
     * @param item the item to be added.
     */
    public void addLast(E item) {
        // TODO
    }

    /**
     * Returns and removes the first item in the list.
     * 
     * @return the first item in the list.
     */
    public E removeFirst() {
        // TODO
        return null;
    }

    /**
     * Returns and removes the last item in the list.
     * 
     * @return the last item in the list.
     */
    public E removeLast() {
        // TODO
        return null;
    }
}