using System;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        Console.WriteLine("Hello World");

    }

    LinkedList list = new LinkedList();

    Node n = new Node(1);   

}

​

class Node

{

    public Node prev = null;

    public Node next = null;

    public int val = -1;

    public Node(int val)

    {

        this.val = val;

    }

}

​

class LinkedList    

{

    //List<Node> list = new List<Node>();

    Node head = null; 

    Node tail = null;

    public LinkedList()

    {

    }

    public void Insert(Node node)

    {

        // insert always at the head

        if(head != null)

        {

            node.next = head;

            head.prev = node;

        }

        head = node;

        //list.Add(node);

    }

    public void Delete(Node node)

    {

        if (node == head)

        {

            head = node.next;

            node.next.prev = null;

        }

        else

        {

            node.next.prev = node.prev;

            node.prev.next = node.next;

        }

    }

    public void reverse (Node node)

    {

        while(node.next != null)

        {

        }

    }

}