[jQuery] Newbie Q: Insert last paragraph just before fourth paragraph?

Hi all-
I suspect this is ridiculously easy.. but I'm lost..
I'm looking for a jquery way of taking the last paragraph (with
class="last") of a many paragraph page and 'inserting' it just before
the fourth paragraph (which does not have a class).
So:

something

<p class="last">something
Is actually seen as: