public class DoublyLinkedList {
	private class NodeDLL {
		int data;
		NodeDLL next = null;
		NodeDLL prev = null;
		public NodeDLL(int data){
			this.data = data;
		}
	}

	NodeDLL head = null;
	NodeDLL tail = null;

	public DoublyLinkedList(){this.head = null; this.tail = null;}

	public void append(int data){
		if (head == null){
			head = new NodeDLL(data);
			tail = head;
		}
		else{
			tail.next = new NodeDLL(data);
			tail.next.prev = tail;
			tail = tail.next;
		}
	}

	public void prepend(int data){
		if (head == null){
			head = new NodeDLL(data);
			tail = head;
		}
		else{
			head.prev = new NodeDLL(data);
			head.prev.next = head;
			head = head.prev;
		}
	}
}