Building 3770

You awake in a mysterious and confusing room. Getting over a daze, you focus on a sign on the wall in front of you: BUILDING 3770. "Where am I?!" you wonder to yourself. You find a dead guy lying in a pool of blood with a saw through his torso to your right. Diagonally from where you are, you see a guy sitting, hunched over, with his arm chained to a wall; he looks weak. Both of them have the same shirt on, and so do you. He tells you to run and escape from the place, and you have to figure out how you're going to manage that.