the right place to put the references to the libraries in C#

Question

Possible Duplicate:
Should Usings be inside or outside the namespace

Hi,

Actually we have two conventions, like
1.

namespace FullFeaturedApp
{
    using System.Web.Mvc;
    using User;

    public class UserManager : Controller{....}
}

2.

using System.Web.Mvc;
using User;
namespace FullFeaturedApp
{
    public class UserManager : Controller
    {
        ....
    }
}

What is the difference between these two systems.