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: dennis kearney (1847–1907) was an american politician who was himself an immigrant from ireland.
Example Output: dennis kearney

Example Input: nellie paulina burgin (july 14, 1930 – september 20, 2014), better known by her stage name polly bergen, was an american actress, singer, television host, and businesswoman.
Example Output: polly bergen

Example Input: louis nirenberg (born 28 february 1925) is a canadian american mathematician.
Example Output:
louis nirenberg