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 timber rattlesnake ("crotalus horridus") is a species of venomous pit vipers.

Ex Output:
timber rattlesnake


Ex Input:
walter rudolf hess (17 march 1881 – 12 august 1973) was a swiss physiologist.

Ex Output:
walter rudolf hess


Ex Input:
a banana split is a type of dessert.

Ex Output:

banana split