Okay, so this is a little bit out there, but what the hey - I know there's some programmer type folks around here. My mission is this: I want to rename this list of files (actually it's much bigger than this) so that there's just a 14-digit number and where there are duplicate numbers I want to add a serial letter after each to differentiate them. I have been unable to fashion a solution from my usual renamer utility, but it also has this "regular expressions" feature which is unfamilar to me. The way I figure this is the only way to seek out duplicate strings.
So for example:
01890000001215 Hopfen 2.jpg
01890000001215 Hopfen Detai.jpg
01890000001215 Hopfen.jpg
I want to result in:
01890000001215a.jpg
01890000001215b.jpg
01890000001215c.jpg
How would I format a regular expression to solve this? Any ideas? Thanks much!

Oh sure, researching this project has gone well beyond the time it would have taken me to just manually type what I wanted, but dang it I wanna learn how to automate this if possible.
01890000001082 Ferienhaus w.jpg
01890000001082.jpg
01890000001083 Ferienhaus r.jpg
01890000001084 Ferienhaus g.jpg
01890000001133 Ladegut.jpg
01890000001137 Ausschneideb.jpg
01890000001137 Werbeplakate.jpg
01890000001138 Ausschneideb.jpg
01890000001138 Werbeplakte.jpg
01890000001139 Ausschneideb.jpg
01890000001139 Fahnen.jpg
01890000001152 Trike 2.jpg
01890000001152 Trike.jpg
01890000001209 Blumentopf S.jpg
01890000001214 1217 1218 12.jpg
01890000001214 Gurken Tomat.jpg
01890000001215 Hopfen 2.jpg
01890000001215 Hopfen Detai.jpg
01890000001215 Hopfen.jpg
01890000001216 Gerste.jpg
01890000001217 Lupinen.jpg
01890000001218 Lupinen.jpg
01890000001219 Dahlien.jpg
01890000001230 Blumentopfe.jpg
01890000001231 Margeriten u.jpg
01890000001232 Rosen und So.jpg
01890000001301 1305 Stimmun.jpg
01890000001301 6141 Dunen .jpg
01890000001301 Trockenes Gr.jpg
01890000001302 Fruhlingsgr.jpg
01890000001303 Sommergras.jpg