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:
the scrotum is the bag that holds the testicles (commonly called "balls") in male mammals.

Ex Output:
scrotum

Ex Input:
l'elisir d'amore is an italian comic opera in two acts.

Ex Output:
l'elisir d'amore

Ex Input:
dr robert anton wilson (january 18, 1932 january 11, 2007) was a futurist thinker, libertarian, and writer.

Ex Output:
robert anton wilson