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
1,622. One to tell the original joke, and the rest to submit give some minor variation of it! For example:
or
He made an illegal ewe turn.
or
Infantry.
or
In sundae school.
or
He was a baaaaaaaaad driver.
or