Search in Google after Wp search

How can i retrieve the string that the user searches in my blog so that i could give him the chance of searching it in Google afterwards?
Try to search something on my website. if nothing is found you´ll have the usual message of “sorry, bla bla”, and also my new “invention” of “try to search Google”.
Unfortunately the user has to type once more the text he was searching..
Can anybody help me?