I need help understanding how to solve this task. I have tried writing the code, but I am not sure why my solution does not work. Could you please explain the approach and point out my mistake?

Hello, I need help with this task. I have tried to solve it by myself, but I am having difficulty understanding the correct approach. I would like to know how to analyze the problem, choose the right solution, and avoid common mistakes. If possible, please explain where my thinking or code is wrong and give me some guidance instead of only providing the final answer. Thank you for your help.