HAProxy reqrep request manipulation

I'm aiming to achieve the following in HAProxy using reqrep; any advice/assistance on how to achieve that would be greatly appreciated :)

Overall, either through request manipulation (reqrep) or another method, I need to perform a rewrite matching the below:

from: subdomain.domain.com/subcategory1/subcategory2/image.jpg

to: subcategory1.domain.com/image.jpg**

Over complicating it, subcategory is not always the same but is always "p" followed by a two digit number, eg. /p1/ or /p21/

Thanks in advance :)