using System;

​

//using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        //Console.WriteLine("Hello World");

        MyStack obj = new MyStack();

        Console.WriteLine("Push " + obj.Push(2));

        Console.WriteLine("Push " + obj.Push(45));

        Console.WriteLine("Push " + obj.Push(20));

        Console.WriteLine("Push " + obj.Push(5));

        obj.PrintStack();

        Console.WriteLine("POP " + obj.Pop().Data);

        Console.WriteLine("POP " + obj.Pop().Data);

        Console.WriteLine("POP " + obj.Pop().Data);

        Console.WriteLine("POP " + obj.Pop().Data);

        Console.WriteLine("POP " + obj.Pop());

        obj.PrintStack();

    }

}

​

public class Node

{

    public Node Next;

    public object Data;

}

​

public class MyStack

{

    //private Node stack;

    private int count;

    private Node top;

    public MyStack()

    {

        this.top = new Node();

    }

​

    private Node GetNewNode(object data)

    {

        return new Node()

        {Data = data};

    }

​

    public Boolean Push(object data)

    {

        Node item = this.GetNewNode(data);

        item.Next = this.top;

        this.top = item;

        return true;

    }

​

    public Node Pop()

    {

        if(this.top!=null){

            Node itemRemoved = this.top;

            this.top =  itemRemoved.Next;   

            return itemRemoved;

        }

        return null;

    }

​

    public void PrintStack()

    {

        Node current = this.top;

        while (current != null)

        {

            Console.WriteLine(current.Data);

            current = current.Next;

        }

    }

}