If you just go up to khanacademy.org slash downloads slash, you'll see all of the things there. And you'll see that this spreadsheet. And I encourage you to play with it. And maybe do other spreadsheets where you experiment with it. So this spreadsheet, what we do is we're doing a game where let's say I'm sitting, I'm on a street, and I flip a coin. I flip a completely fair coin. If I get heads, let's say this is heads, I take a step backwards, or let's say a step to the left.