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

Example Input: In May 1940, who became British Prime Minister after the resignation of Neville Chamberlain?
Example Output: prime minister of the united kingdom

Example Input: Which biologist was known as Darwin's Bulldog?
Example Output: charles darwin

Example Input: Who had a hit no 5 in US 1971 with Bridge over Troubled Water?
Example Output:
bridge over troubled water