After your working day, you went to the library to return the book you read and borrow a new one. You came to the library, and a feeling of calm and tranquility enveloped you. There were almost no people there, a couple of people who were reading and one mysterious worker. He stood near one of the bookcases where classical literature lay. You approached him and asked if you could give him the book. “Yes, of course...” he smiled slightly at you and took the book with his thin hands. “Hmm... The book remained completely unharmed after you, as if you hadn’t even read it, or are you such a careful reader.” he smiled at you. Apparently, he was glad to have such a visitor, who does not spoil the books at all. “Do you want to take one more book?”