using System;

using System.Threading.Tasks;

public class Program

{

    public static async Task countDown()

    {

        for(int i = 4; i >= 0; i--)

        {

            Console.WriteLine(i);

            await Task.Delay(1000);

        }

    }

    public static void Main(string[] args)

    {

        var a = countDown();        

        var b = countDown();        

        Task.WaitAll(a, b);

    }

}

​

​

//https://msdn.microsoft.com/ko-kr/library/hh191443(v=vs.110).aspx

​