using System;

public class ListNode {

     public int val;

     public ListNode next;

     public ListNode(int x) { val = x; }

     }

public class Program

{

    public static void Main()

    {

        Console.WriteLine("Hello World");

    }

    public bool HasCycle(ListNode head) {

         ListNode slow=head;

        ListNode fast=head;

        while(fast!=null && fast.next!=null)

        {

            slow=slow.next;

            fast=fast.next.next;

            if(slow==fast) return true;

        }

        return false;   

    }

}