using System;

using System.Threading;

using System.Threading.Tasks;

using System.Diagnostics;

​

public class Program

{

    static async Task MySleep() {

        Console.WriteLine("Begin sleep");

        Task.Delay(1000);

    }

    static async Task Do() {

        Console.WriteLine("Do");

        Thread.Sleep(1000);

        await MySleep();

    }

    static async Task MainAsync() {

        var now = DateTimeOffset.Now;

        var t1 = Do();

        var t2 = Do();

        await Task.WhenAll(t1, t2);

        Console.WriteLine(DateTimeOffset.Now - now);

    }

    public static void Main()

    {

        MainAsync().GetAwaiter().GetResult();

    }

}