using System;

public class Program

{

    public static void Main()

    {

        Console.Write("choose between green/yellow/red: ");

        string currentAmpel = Console.ReadLine();

        TrafficLight(currentAmpel);

    }

    public static void TrafficLight(string signal)  {   

        switch(signal)

        {

            case "red":

                Console.WriteLine("it will soon get green");

                break;              

            case "green":

                Console.WriteLine("it will soon get yellow");

                break;

            case "yellow":

                Console.WriteLine("it will soon get red");

                break;

            default:

                Console.WriteLine("invalid input");

                break;

        }

    }

}