Five: one to handle the bulb and four to contemplate how David Sanborn would've done it.
or
By paying them to cheer for him during campaign events.
or
6: 2 to screw in the bulb and 4 to testify that it was lit from the moment they began screwing.
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