using System;

using System.Net.Http;

using System.Threading;

using System.Threading.Tasks;

public class Program

{

    public static async Task Main(string[] args)

    {

        var task1 = Foo1(1);

        var task2 = Foo1(2);

        var task3 = Foo1(3);

​

        Console.WriteLine("before");

        Thread.Sleep(TimeSpan.FromSeconds(5));

        Console.WriteLine("Main");

​

        await task1;

        await task2;

        await task3;

        Console.WriteLine("end");

    }

​

    private static async Task Foo(int taskNum)

    {

        await Foo1x(taskNum);

    }

    private static Task Foo1(int taskNum)

    {

        return Foo1x(taskNum);

    }

    private static async Task Foo1x(int taskNum)

    {

        Console.WriteLine($"{taskNum} start");

        await Task.Delay(TimeSpan.FromSeconds(2));

        Console.WriteLine($"{taskNum} middle");

        await Task.Delay(TimeSpan.FromSeconds(3));

        Console.WriteLine($"{taskNum} finish");

    }

}