How to get json response using system.net.webrequest in c#?

I need to get json data from an external domain.
I used WebRequest to get the response from a website.
Here's the code:

var request = WebRequest.Create(url);
string text;
var response = (HttpWebResponse) request.GetResponse();

using (var sr = new StreamReader(response.GetResponseStream()))
{
    text = sr.ReadToEnd();
}

Does anyone know why I can't get the json data?