Because he was under cover.
or
Three: One to screw it in, and the other two to help him down off the keg.
or
1,000,001: One to change the bulb and 1,000,000 to rebuild civilization to the point where they need light bulbs again.
or
Drinking, bathing, washing, swimming, etc.
or
None: they just deny that the bulb ever went out in the first place.
or
It's time to go to sweep.
or