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:
songkran is a festival held every year in thailand on april 13.

Ex Output:
songkran

Ex Input:
henan is a province of the people's republic of china.

Ex Output:
henan

Ex Input:
dead calm is an american novel that was written in 1963.

Ex Output:
dead calm