How to loose 5,10 or 20 kg on first day at Gym

This fat guy sees an ad for a new gym guaranteeing to
reduce anyone's
weight by 5, 10 or 20 kilograms on the first day. So
he goes and tells
them he wants to lose 5 kg. They lead him into a huge
gym with all kinds
of ropes and parallel bars and ladders and tell him to
wait a minute.
He's standing there when on the far side of the gym a
door opens and out
steps a beautiful girl, with a sign saying
"If you catch me, I'm yours."

He starts running, and just as he gets close, she
starts picking up
speed.

Before he knows it, he's running all over the gym, up
the ladders, down
the ladders, across the parallel bars, here and there.
And just as he's
about to catch the blonde, pop, she disappears through
a door. In comes
the manager who lead him to the showers, and then
weigh him. Sure
enough, he lost exactly 5 kg.

He's back on the street and starts to think.

"Jesus, I was so close to catching her. If I had a
little more time..."

So he races back to the gym and says, "I want to lose
20 more kg."

"No problem," says the manager.

Again he is led to the large gym. This time he's
standing by the door
when it opens. Out comes a gorilla with a sign

"If I catch you, you're mine."