Three:
One to write the light bulb removal program,
one to write the light bulb insertion program, and
one to act as a light bulb administrator to make sure nobody else tries to change the light bulb at the same time.
or
First he lies on one side, then he lies on the other.
or
Microwaves.
or
The bartender offers him a warm smile and says, "For you, no charge".
or