using System;

using System.Threading;

public class Program

{

    public static void Main()

    {

        var counterThread = new Thread(countThread);

        counterThread.Start();

        var counterdownThread = new Thread(countdownThread);

        counterdownThread.Start();

        Console.ReadLine();

    }

​

        static void countThread(){

        for (int i = 1; i< 5; i++){

            Console.WriteLine($"Counter thread {Thread.CurrentThread.ManagedThreadId} i :{i}");

            Thread.Sleep(1000);

        }

    }

    static void countdownThread(){

        for (int i = 5; i>0; i--){

            Console.WriteLine($"Countdown thread {Thread.CurrentThread.ManagedThreadId} i :{i}");

            Thread.Sleep(1000);

        }

    }

}