To run the code, download the folder with books from https://drive.google.com/drive/folders/1V2rO6-b9ynTZu-cVAdK1WQNrpoNIK9w6?usp=sharing and add the resulting fb2/ folder to the project root.
up-to-date collection (fb2): https://drive.google.com/file/d/1vVA1G26Bgs_cEqeuVB6rGZ0gv3CCcQ_I/view?usp=sharing