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: the world conference of life and work was an ecumenic conference.
Example Output: world conference of life and work

Example Input: habib thiam (21 january 1933 – 26 june 2017) was a senegalese politician.
Example Output: habib thiam

Example Input: the agnatha (greek = 'no jaws') are a superclass of vertebrates.
Example Output:
agnatha