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:
altoids are a brand of breath mints and candies that have been sold since the 1800s.

Ex Output:
altoids

Ex Input:
the occipital lobe is the back part of a mammal's brain.

Ex Output:
occipital lobe

Ex Input:
tropical storm allison was one of the worst tropical storms in the history of the united states.

Ex Output:
tropical storm allison