There is only one room to check on the third floor. Room 304 has some pistol
bullets in the bedroom, but that's it. Room 303's key is missing from the
ring, and your room is still stuck. Put any remaining red papers under your
door and proceed through the hole in the hall back to your room. In your room,
feel free to put away the apartment keys, as they're all unlocked. Then, read
all the red pieces of paper from under your door. You will realize that the
key to Room 303 is now magically next to your bed, between the bed and the
window. Now, hurry back through the hole, and back up to Room 303. Use the key
and head on in. You'll see a cutscene with yet another number.