A man discovers a wallet that has $700 inside.

A man finds a wallet with $700 inside. A few days later, he sees a notice from a rich man who lost his wallet and is offering a $50 reward to whoever returns it. The man finds the owner and hands back the wallet. The rich man counts the money and says, “I see you’ve already taken your reward.”
The poor man is confused and asks, “What do you mean?”