Parsing data using GDataXMLDocument

{type:1 name:s:Envelope xml:"<s:Envelope 
xmlns:s="http://ift.tt/sVJIaE"><s:Body><ValidateUserResponse 
xmlns="http://Mobile/2011"><ValidateUserResult>false</ValidateUserResult
</ValidateUserResponse></s:Body></s:Envelope>"}

I have the following xml that I am trying to retrieve ValidateUserResult from. How would I go about doing this in XPath?

Ive already parsed the data using:

GDataXMLDocument *docc = [[GDataXMLDocument alloc] initWithData:data options:0 error:&error];

Then I tried

NSArray *resultNodes = [docc nodesForXPath:@"//s:Envelope/s:Body/ValidateUserResponse/ValidateUserResult" error:&error];

but I'm getting nil. What would the correct syntax be?