using System;

using System.Threading;

using System.Threading.Tasks;

public class Program

{

    public static async Task Main()

    { 

        Console.WriteLine("Hello World");

        await TestAsync();

        Console.WriteLine("Goodbye World");

    }

    private static async Task TestAsync()

    {

        var t1 = DoStuffAsync(1);

        var t2 = t1.ContinueWith(x => DoSyncStuff(2));

        Console.WriteLine("Caller processing  " + DateTime.Now);

        Console.WriteLine("Task " + await t1 + " is done.    " + DateTime.Now);

        await t2;

        Console.WriteLine("Caller finished    " + DateTime.Now);

    }

    private static void DoSyncStuff(int number)

    {

        Console.WriteLine($"{number} will sync sleep at    " + DateTime.Now);

        Thread.Sleep(1000);  //synchronous wait

        Console.WriteLine($"{number} done sync sleeping at " + DateTime.Now);

    }

    private static async Task<int> DoStuffAsync(int number)

    {

        Console.WriteLine($"{number} task starting at " + DateTime.Now);

        var task = Task.Delay(2000);

        Console.WriteLine($"{number} task created  at " + DateTime.Now);

        Thread.Sleep(1000);  //synchronous wait

        Console.WriteLine($"{number} done sleeping at " + DateTime.Now);

        await task;

        Console.WriteLine($"{number} completed     at " + DateTime.Now);

        return number;

​

    }

}