Rewrite Threads from vbseo (Need help with one rule)

Hi experts ;)

i need a mod_rewrite (Apache) rule to rewrite my threads from vbseo to xenforo.

from: /f123/titel-of-thread-ID/

to: /thema/titel-of-thread.ID/

I need to rewrite all URIs starting with f followed by 1 to 3 digits and have to exchange the "dash" -ID at the end to "dot" .ID
ID may be 1 to 5 digits.

The one who fixes my Problem gets a link to one of his projects in a "thank you" thread posted on our xenforo.

Thank you...