# A snail is at the bottom of a 20 meters deep pit. Every day the snail climbs 5 meters upwards, but at night, it slides 4 meters back downwards.

How many days does it take before the snail reaches the top of the pit?

On the first day, the snail reaches a height of 5 meters and slides down 4 meters at night, and thus ends at a height of 1 meter.

On the second day, he reaches 6 meters, but slides back to 2 meters.

On the third day, he reaches 7 meters, but slides back to 3 meters.

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