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: metis is the goddess of wisdom in greek mythology.
Example Output: metis

Example Input: a sonata is a piece of music for one instrument or one instrument with another instrument accompanying.
Example Output: sonata

Example Input: bios, computing, stands for basic input/output system.
Example Output:
bios