Gentlemen of Fortune

The movie follows the story of an amiable kindergarten director named Troshkin who looks exactly like a cruel criminal nicknamed Docent (Доцент, literally associate professor) that has stolen Alexander the Great's helmet at an archaeological excavation. Docent and his gang are caught by police, but Docent is imprisoned in a different jail than his mates. Since Troshkin looks identical to Docent, the police send him undercover to prison with the real criminals to get information about the stolen helmet. He must pretend to be the real felon Docent, so in order to be convincing, Troshkin, a well-educated and good-natured man, has to learn slang and manners of criminals. Read more on Wikipedia.