Five. One to screw it in and four to tell him how bitchin' he looked doing it.
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
Five. Four to decide which way the bulb ought to turn, and . . .
or
Put it in a glass with some ice cream and root beer.
or