Just one, but he'll also want to do something about your nose.
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
Two — one to screw it most of the way in and the other to give it a surprise twist at the end.
or
but it was a little Chewie.
or
Because he was feeling crumby.
or
A traffic jam.
or