using System;

using System.Threading.Tasks;

public class Program

{

    static private Task t;

    static int i=0;

    static object l=new object();

    public static void Main()

    {

        var action = (object unused) => 

            {

                int local;

                lock (l)

                {

                    local=i++;

                }

                Console.WriteLine($"Hello World {local}");

            };  

    var action1 = (object unused) => Task.Run(() =>

            {

                int local;

                lock (l)

                {

                    local=i++;

                }

                Console.WriteLine($"Hello World {local}");

            }); 

        t=Task.Run(()=>action(null));

        t=t.ContinueWith(action);

        t=t.ContinueWith(action);

        t=t.ContinueWith(action);

        t=t.ContinueWith(action);

        t=t.ContinueWith(action);

        t=t.ContinueWith(action);

        t=t.ContinueWith(action);

        t=t.ContinueWith(action);

        t=t.ContinueWith(action);

        t=t.ContinueWith(action);

        t.Wait();

        if (t.IsCompleted)

            i=1000;

        t=t.ContinueWith(action);

        t=t.ContinueWith(action);

        t=t.ContinueWith(action);

        t=t.ContinueWith(action);

        t=t.ContinueWith(action);

        t=t.ContinueWith(action);

        t=t.ContinueWith(action);

        t=t.ContinueWith(action);

        t=t.ContinueWith(action);

        t=t.ContinueWith(action);

        t.Wait();

    }

}