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.

Input: Consider Input: a viola is a musical instrument which is similar to the violin and cello.

Output: viola


Input: Consider Input: a dandelion is a flower.

Output: dandelion


Input: Consider Input: the spanish treasure fleet, or west indies fleet from spanish "flota de indias", was a convoy system adopted by the spanish empire from 1566 to 1790.


Output: spanish treasure fleet