Три рубля

Gringotts Bank Notes were official negotiable promissory notes issued by Gringotts Wizarding Bank and available at the Gringotts Money Exchange at Carkitt Market in Diagon Alley. Redeemable at many establishments throughout wizarding Britain, Muggles were able to exchange their currency for bank notes that they could later use to make their purchases within the magical community.

Those goblins are sneaky people. They manage to put the Muggle money back into circulation. They are like “fences” -- British slang, do you understand it?