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: island of the blue dolphins is an american book written for children by scott o'dell.
Example Output: island of the blue dolphins

Example Input: ammonium carbonate, also known as baker's ammonia or sal volatile, is a chemical compound.
Example Output: ammonium carbonate

Example Input: eosinophil granulocytes, usually called "eosinophils" or "eosinophiles", are granulocyte white blood cells that fight off certain parasites and infections in vertebrates.
Example Output:
eosinophil granulocyte