using System;

class Node 
{
    public int data;
    public Node next;
    
    public Node(int value) {
        data = value;
        next = null;
    }
}
class SLList 
{
    private Node head = null;
    
    public void AddLeft(int val)
    {
        Node newNode = new Node(val);
        newNode.next = head;
        head = newNode;
    }
    public void Reverse() 
    {
        Node prev = null;
        Node next = null;
        Node curr = head;
        while (curr != null) {
            next = curr.next;
            curr.next = prev;
            prev = curr;
            curr = next;
        }
        head = prev;
    }
    public void Print()
    {
        Node temp = head;
        while (temp != null) 
        {
            Console.Write(temp.data + " -> ");
            temp = temp.next;
        }
        Console.WriteLine("null");
    }
}
public class MainClass
{
    public static void Main(string[] args)
    {
        SLList list = new SLList();
        list.AddLeft(50);
        list.AddLeft(40);
        list.AddLeft(30);
        list.AddLeft(20);
        list.AddLeft(10);
        list.Print();
        list.Reverse();
        list.Print();
    }
}