We'll see about that."
or
Five: One to change the bulb and four to pull the ladder out from under him/her.
or
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
Weeeeeeeeeeeeeeeeeeeeeeeeeee
or
Only two, but the hard part is getting them into the light bulb.
or