using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace Stack
{
    class Stack
    {
        Node start = null;

        public void push(int val)
        {
            Node tmp = new Node(val);
            tmp.next = start;
            start = tmp;
        }

        public void pop()
        {
            if (start == null)
            {
                return;
            }

            start = start.next;
        }

        public int top()
        {
            if (start == null)
            {
                return 0;
            }

            return start.info;
        }


        public bool empty()
        {
            return (start == null);
        }

    }
}