cash money

You're walking down the street with a friend/acquaintance, and money falls out of their pocket. You're real tight for money, and you know they have a lot, so do you pick the money up, let them know they dropped it and return it to them? Or do you pick the money up, and casually put it in your pocket, and if they notice that they lost money later on, say "yeah, that sucks" and act sympathetic?