There is a well with a depth of15m. A frog jumped up from the bottom of the well, jumping 2 meters in each direction and retreating 1 meter. Ask a few more times and you'll jump. The answer is: 14.

Jump 2 meters in each direction, retreat 1 m, and actually rise 2- 1 = 1 m each time, 13 times * * rise13 times1=13 meters,/