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
As many as possible, and don't *ask* what they do with the old bulb.
or
A waist of time!
or
10. One to hold the bulb and nine to rotate the ladder.
or