Permalink Structure changed, looking for rewrite help

Recently I changed my blog from the standard /%year%/%monthnum%/%day%/%postname%/ to /%postname%/

However the blog is 5 years old and I’d be able to not get 404 errors on “old” links. don’t really want to overload the site with plugins, henc eI thought it would be easy to add a rewrite rule in .htaccess

However I am somewhat stuck and would appreciate some help.

Example link
old: http://www.myrddin.de/2011/01/19/enhancement-shaman-soloable-bosses/
new: http://www.myrddin.de/enhancement-shaman-soloable-bosses/

I thought that a simple

RewriteRule /([0-9][0-9][0-9][0-9])$/([0-9][0-9])$/([0-9][0-9])$/(.*)/ /$4/ [R]

Would do the trick, but it doesn’t. Can anyone point me the right way? thanks