Finding One Hundred Dollars

There was this guy on his way to the grocery store. It's a nice summer day, and he's enjoying the breeze.

And he sees a small scrap of paper on the sidewalk. He can't make out what it is.
Oh, wait a second.

It's a hundred dollar bill.

He looks at the hundred dollar bill. There's no-one around except for a few kids riding their bikes, and an old lady down the block pruning her garden.

What does he do?

Pretend this guy was you -- just like any other Jane or John Doe, walking to the grocery store, finding a lone Hundred Dollar Bill on the pavement. What would you do?