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.

Example Input: a brinicle is a column of ice that forms in seawater.
Example Output: brinicle

Example Input: the nissan maxima is an automobile produced by nissan motor company in seven generations since 1981.
Example Output: nissan maxima

Example Input: the global hunger index is a measurement to measure the hunger situation in a country.
Example Output:
global hunger index