Mr. Bean v/s Einstein

Mr. Bean v/s Einstein:
.
.
Einstein & Mr.Bean sitting next to
each other on a long flight..
Einstein says,"Let's play a game.. I
will
ask you a question,if you don't
know
the answer,you pay me only $5 and
if I
don't know the answer,I will pay you
$500.."
Einstein asks the first question:
What's the distance from the Earth
to
the Moon..?
Mr.Bean doesn't say a word,reaches
his pocket,pulls out a $5..
Now,it's Mr.Bean's turn..
He asks Einstein: What goes up a
hill
with 3 legs and comes down on 4
legs..?
Einstein searches the net and asks
all
his smart friends.. After an hour he
gives Mr.Bean $500..
Einstein going nuts and asks: Well,so
what goes up a hill with three legs
and comes down with four..?
Mr.Bean reaches his pocket and
gives
Einstein 5$