One; after reflecting in the twilight on the merit of the previous bulb.
or
Five: One to change the bulb and four to pull the ladder out from under him/her.
or
Twenty. One to hold the bulb, two to turn the ladder, and 17 to be on the guest list.
or
A New Jersey.
or
Three. One to climb the ladder while the second kicks the ladder out from under her. And the third to say, "I knew that was too high for you dear."
or