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: skagit valley is a valley in washington in the united states.
Example Output: skagit valley

Example Input: escape velocity is the initial speed that something would need to completely escape the gravity of a large body, like a star or a planet (such as the earth), by mere inertia.
Example Output: escape velocity

Example Input: cape hatteras is a cape on the coast of north carolina.
Example Output:
cape hatteras