using System;

using System.Threading.Tasks;

​

class Program {

    static void Main(string[] args) {

        Console.WriteLine("Hello, world!");

        new Program().Run().Wait();

    }

​

    async Task Run()

    {

        await Run1();

        await Run2();

    }

​

    async Task Run1()

    {

        Console.WriteLine("Run 1");

        await A();

        await B();

    }

​

    async Task Run2()

    {

        Console.WriteLine("Run 2");

        var a = A();

        var b = B();

​

        await a;

        await b;

    }

​

    async Task A()

    {

        Console.WriteLine("A starting");

        await Task.Delay(1000);

        Console.WriteLine("A ending");

    }

​

    async Task B()

    {

        Console.WriteLine("B starting");

        await Task.Delay(1000);

        Console.WriteLine("B ending");

    }

}