my Automation code : program does not contain a static main method suitable for an entry point when i'm working C# with selenium web driver

In C# Selenium web driver script I'm getting an error.

Here is my C# Selenium web driver code:

using System;
using Microsoft.VisualStudio.TestTools.UnitTesting;
using OpenQA.Selenium;
using OpenQA.Selenium.Firefox;

namespace UnitTestProject3
{
    [TestClass]
    public class testrammi
    {
        [TestMethod]
        public void SetupDllTest()
        {
            IWebDriver driver = new FirefoxDriver();
            driver.Navigate().GoToUrl("docs.seleniumhq.org /download/");
        }
    }
}