Scarab Beetle from Serbia

Subject:  Pentodon species identification
Geographic location of the bug:  Žagubica, Serbia.
Date: 12/20/2018
Time: 01:16 PM EDT
Your letter to the bugman:  Thanks to iNaturalist community I found out that the genus of this Coleoptera is Pentodon spp. but I can’t figure out what species it is because all of them look the same to me, and I couldn’t find any keys for this genus online. The specimen was collected in June 2017 (not by me). According this site: http://bioras.petnica.rs/pretraga.php?searchtext=pentodon
there are only 3 species (and one subspecies) in Serbia, so it’s likely one of them, but again they look practically the same to me. The insect is just under 2 cm. I can try to take additional photos if necessary.
How you want your letter signed:  Regards, Mihajlo

Dear Mihajlo,
We are not familiar with this genus of Scarab Beetles, but since it is in the subfamily Dynastinae, the Rhinoceros Beetles, we suspect this is a female since most males in this subfamily have fantastic horns.  Females present an additional identification challenge as they are often quite similar looking.  Perhaps one of our readers will be able to provide additional information.  We get so few submissions from Serbia.

Thank you for your reply. In the meantime I found out what species it is. Someone from iNaturalist who is also from Serbia said that there is actually only one species in Serbia which is Pentodon idiota.
Regards,
Mihajlo