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:
mohamed allalou (born september 28, 1973) is an algerian boxer.

Ex Output:
mohamed allalou


Ex Input:
a breed is a domesticated race or type of an animal or plant.

Ex Output:
breed


Ex Input:
the lanthanide (or lanthanoid) series is a group of 15 elements that have atomic numbers 57 to 71.

Ex Output:

lanthanide