You probably die. X=238m. Think about it, 50 degrees is pretty close to 45 degrees, so they're not much farther than your flat is up high. The zombies move at a respectable 2m/s (Usain Bolt is a zombie, huh?) so you have about 119 seconds to work with, in which time you must grab food and descend roughly 50 stories to exit the building before they get there. Don't take the elevator. And when you get to the bottom of the stairs I hope you're not winded, because you need to haul ass away from those highly motivated zombies. So yeah, option 3 I guess, but you'll probably die anyway.