Generate a topic word for the given sentence. A topic word is usually the name of a person, place, animal, concept or object the sentence is focusing on.

Ex Input:
a mathematician's apology is a book about mathematics which was written in 1940.

Ex Output:
a mathematician's apology


Ex Input:
the usl w-league is a national women's soccer league.

Ex Output:
w-league


Ex Input:
sebastian vettel (born 3 july 1987 in heppenheim) is a german race car driver.

Ex Output:

sebastian vettel