CS0103 The name 'Assert' does not exist in the current context in console appliacation

[vinay kumar]

i am using the below code 

using OpenQA.Selenium;

using OpenQA.Selenium.Chrome;

using OpenQA.Selenium.Firefox;

using OpenQA.Selenium.IE;

using OpenQA.Selenium.Remote;

namespace ConsoleApplication2

{

    class Program

    {

        static void Main(string[] args)

        {

            IWebDriver obj = new ChromeDriver();

            obj.Url=("https://www.compare.com");

            //  string titlelength = obj.Title;

            string pageurl = obj.Url;

           // obj.Navigate().GoToUrl("https://www.compare.com");

            string pagesource1 = obj.PageSource;

            Assert.IsTrue(obj.PageSource.Contains("GTM-5SL7R9"),"test");

            //Console.WriteLine(pagesource);

            // Console.WriteLine(titlelength);

            Console.WriteLine(pagesource1);

            obj.FindElement(By.CssSelector("#mainContainer > div.row > div > div > div > div > div > div > form > div > input")).SendKeys("75001");

            obj.FindElement(By.CssSelector("#mainContainer > div.row > div > div > div > div > div > div > form > div > div > input")).Click();

            

       

            obj.Close();

            Console.ReadLine();

and gettign the errror. it is an console application .kindly help