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:
defibrillation is the act of defibrillating the heart to treat the heart when it is not pushing blood because the heart muscle is not working in any pattern.

Ex Output:
defibrillation


Ex Input:
ash ketchum (satoshi in japanese) is a character from the "pokémon" anime.

Ex Output:
ash ketchum


Ex Input:
the descent of man, and selection in relation to sex is a book by charles darwin, first published in 1871.

Ex Output:

the descent of man