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 Q]: the chinese postman problem is a mathematical problem of graph theory.
[EX A]: chinese postman problem

[EX Q]: norio yoshimizu (吉水 法生, yoshimizu norio, born august 21, 1946) is a former japanese football player.
[EX A]: norio yoshimizu

[EX Q]: masakuni yamamoto (山本 昌邦, yamamoto masakuni, born april 4, 1958) is a former japanese football player.
[EX A]:
masakuni yamamoto