One, if it knows its own Goedel number.
or
you need to take a long, hard look at yourself.
or
Many hands make light work.
or
Only one, but it may take upwards of five years for him to get it done.
or
The League of Extraordinary Con Men.
or
Three, One to climb the ladder. One to shake it. And one to sue the ladder company.
or
A brick layer!
or
Ice cream.
or
Use a pen.
or
Because it would fall over if it lifted the other one.
or