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: 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: corrosion is the breakdown of materials due to chemical reactions.
Example Output: corrosion

Example Input: jamal woolard (born july 8, 1975) is an american stand-up comedian, actor, rapper, and comedian.
Example Output:
jamal woolard