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
In Washington, D.C.
or
Two. One to assure the everything possible is being done while the other screws the bulb into the water faucet.
or
Three: One to screw it in, and the other two to help him down off the keg.
or