Five. One to change the bulb and eleven to say they could do it faster.
or
Seven. One to change it and the other six to sing about how good the old one was.
or
What's the use, they'd still have bear feet
or
Because all the fans left!
or
I said, "I can't make Tuesdays"
or
1,000,001: One to change the bulb and 1,000,000 to rebuild civilization to the point where they need light bulbs again.
or