A 50-word story about a mathematician

When did the snail climb up the well?

A snail accidentally fell into a dry well. It lay down at the bottom of the well and cried. A leprous (

lai) toad crawled over and said angrily to the snail: "Stop crying, little brother! It's useless to cry. The wall of this well is too high. If you fall here, you will have to fall here." This life. I have lived here for many years, and I have not seen the sun for a long time, let alone want to eat swan meat!" The snail looked at the old and ugly toad and thought to himself: "How beautiful the world outside the well is. "Ah, I can never live in a dark and cold well like that!" The snail said to the toad, "Uncle Legg, I must climb up!" "How deep is this well?" Hahaha... What a joke! This well is 10 meters deep. How can you climb up at such a young age and with such a heavy shell on your back? "I am not afraid of hardship or fatigue. I can always climb a section every day." Climb out!" The next day, the snail was full of food and drank enough water, and began to climb up the well wall. It kept climbing, and finally climbed 5 meters in the evening. The snail was very happy and thought: "At this speed, I will be able to climb up tomorrow evening." Thinking about it, it fell asleep unknowingly. In the morning, the snail was awakened by a snoring sound. At first glance, it turned out that the leprous uncle was still sleeping. It was startled: "Why am I so close to the bottom of the well?" It turned out that the snail slid down 4 meters from the well wall after falling asleep. The snail sighed, gritted his teeth and began to climb up again. In the evening, I climbed another 5 meters, but at night the snail slid down another 4 meters. Climbing and crawling, the snail finally climbed onto the well platform. Children, can you guess how many days it takes a snail to climb up the well platform?