Burger King is running a clever promotion in order to get people to use its mobile app. You can buy a Whopper for only one cent using the app if the Burger King you are buying it from is within 600 feet of a McDonald’s, reports CNBC. The app uses geofencing to determine the user’s location to a McDonald’s, and if they are within 600 feet, the deal will be enabled. Once they order the one-penny Whopper in the app, the app will give them directions to the nearby Burger King where they can pick their order up.