Nikola likes to categorize everything in sight. One time Stephan gave him a label maker for his birthday, and the robots were peeling labels off of every surface in the ship for weeks. He has since categorized all the reagents in his laboratory, books in the library and notes on the desk. But then he learned about Python dictionaries, and categorized all the possible configurations for Sophia’s drones. Now the files are organized in a deep nested structure, but Sophia doesn’t like this. Let's help Sophia to flatten these dictionaries.

Python dictionaries are a convenient data type to store and process configurations. They allow you to store data by keys to create nested structures. You are given a dictionary where the keys are strings and the values are strings or dictionaries. The goal is flatten the dictionary, but save the structures in the keys. The result should...