Combine “google cache search” with “google I’m Feeling Lucky”

Question

This get the cached page of a site

http://webcache.googleusercontent.com/search?q=cache:[your site]

This get the first site of a google search results aka I’m Feeling Lucky

http://google.com/search?btnI=1&q=[your keyword]

How i can combine this two? I want to get the cached version of the first site of google search result.