title: Bad request 400 for json
body: <p>I am trying to export to file the json output of a url.  But starting with parsing the json output, I got an error of Bad request.  I can't understand why, because when i manually input the url on web, it has a valid result.</p>
  
  <pre><code>using System;
  using System.IO;
  using System.Web;
  using System.Net;
  
  namespace web
  {
      class Program
      {
          static void Main(string[] args)
          {
              var json = new WebClient().DownloadString("http://steamcommunity.com/market/pricehistory/?country=DE&amp;currency=3&amp;appid=570&amp;market_hash_name=Helm%20of%20the%20Guardian%20Construct");
              Console.WriteLine(json);
              Console.ReadLine();
          }
      }
  }
  </code></pre>