You eat a 200-Cal (=200,000 cal, with 1 cal = 4.2 J) lean hamburger for lunch. To burn it all off, you decide to run stairs up a tall building. Suppose you weigh 145 lbs (about 65 kg, or 640 Newtons), and each flight of stairs (from one floor to the next) has a vertical distance of 8 m. If you assume that the amount of energy you burn is equal to the work you do against gravity (mgh) to pull yourself up, then approximately how many stories do you need to climb to completely "burn off" that hamburger?