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.

Ex Input:
eric s. raymond (often called esr; born 4 december 1957) is an american writer and computer programmer.

Ex Output:
eric s. raymond

Ex Input:
absolute truth is something that is true at all times and in all places.

Ex Output:
absolute truth

Ex Input:
the great western main line is a main line railway in england, that runs westwards from london paddington to bristol temple meads.

Ex Output:
great western main line