1)Take off a torch before enter a door.
2) Enter a door before that you took off a torch
3) You will appear at other door. Take off a torch next to this door.
4) Walk up to other door (a torch burns near that), take off a torch and enter.
5) Take off a torch near a that door from that you went out. And will repeat a point 4. Take off torches near those doors in that you entered and went out. Thus you will pass to the exit.