If you find a wad of $100 is it yours to keep?

If you are convinced that you should keep $100 that you found,you are loco.  It would be rude to grab a wad of money($100) and run.  If you find something that is not yours ,and very valuble , bring it straight to the police. Say there is a  decent bike that you have wanted for about a month and costs $90 and you want it really badly but don’t want to feel guilty about steeling it and because you know it would make the person who lost the money feel very upset.