Erro ao executar o código.

Bom dia professor, ao executar o código abaixo, o visual estúdio está exibindo o erro

(OpenQA.Selenium.DriverServiceNotFoundException: 'The geckodriver.exe file does not exist in the current directory or in a directory on the PATH environment variable. The driver can be downloaded at https://github.com/mozilla/geckodriver/releases.') , contudo já baixei o  geckodriver já fui editar "variável de ambiente" (path) e coloquei o caminha (c:\geckodriver.exe) mais ainda está com erro.




using OpenQA.Selenium;
using OpenQA.Selenium.Firefox;
using OpenQA.Selenium.Support.UI;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace testeAutomatizado
{
    class Program
    {


         public static void Main(string[] args)

        {

            //FirefoxDriverService service = FirefoxDriverService.CreateDefaultService();
            //service.FirefoxBinaryPath = @"C:\Program Files\Mozilla Firefox\firefox.exe";



               IWebDriver driver = new FirefoxDriver();
            driver.Navigate().GoToUrl("www.google.com.br");



            IWebElement campoTexto = driver.FindElement(By.Name("q"));
            campoTexto.SendKeys("caelum");


            campoTexto.Submit();

            driver.Close();

        }
    }
}