You got a new guard offer yesterday. Now you are at the company, and your boss asks you to stand at somewhere to do your job -- guard.
You can treat the building as a simple polygon, and your job is finding a position to make sure that you can see the largest area. Please notice that, you have a range of vision, that you cannot see what is out of that range. The wall of building can also block your sight.
Look at that image; if you stand at the middle then you can see the gray area.