There are some balloons on the first stair, people usually want to step on it. When people step on the balloon of the first floor, another balloon will emerge on the next few stairs. All the balloons not emerge on one straight line, so it will let people stride larger step. This makes people consume more energy.
Catching up
When people climbing up stairs, there is a shadow in front of him. The shadow can be an animal, footprints or the record holder. Every time when people want to catch up the shadow, the shadow move further, the people catch up the shadow, the record will change.
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