reading root attribute in a XML using XPathNavigator

I am a new bie to using XPathNavigator and trying to read attribute present in the root. In the below example, it is AppPlatformVersion. I need to read the value 8.0 using XPathNavigator in C#

XPathDocument d =newXPathDocument(reader);XPathNavigator n = d.CreateNavigator;

 <Deployment xmlns="http://schemas.microsoft.com/windowsphone/2012/deployment" AppPlatformVersion="8.0"> </Deployment>

Can any one help how to extract the root attribute using C#?

Thanks

Sahasra