Given a factoid/trivia type question, generate the topic of the question. The topic is the entity the question talks about.

Example Input: Mr Barkis, Edward Murdstone and Tommy Traddles are all characters in which Charles Dickens novel?
Example Output: charles dickens

Example Input: Who directed the film Black Swan (in ballet)?
Example Output: black swan

Example Input: What is the Greek name for Bacchus the god of wine and revelry?
Example Output:
bacchus