Rope Trick

You're trapped in the Prison Tower of Contrivances. Fortunately, you've managed to pry open bars on the window to your cell. Unfortunately, the window is half way up the two hundred foot tall tower.

Conveniently, two fifty-foot ropes are tied to two iron rings in the ceiling of your fifty-foot tall cell. The iron rings (and consequently the ropes) are about a foot apart.

Your confinement has weakened your bones somewhat, so you cannot safely fall more than a few feet without risking serious injury. But your upper-body strength and climbing skills are top-notch.

Armed only with a pocket knife, how much of the rope can you liberate to aid in your escape?