instruction:
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.
question:
the chinese postman problem is a mathematical problem of graph theory.
answer:
chinese postman problem

question:
gossliwil is a former municipality in the district bucheggberg, in the canton of solothurn, switzerland.
answer:
gossliwil

question:
middle c is the name given to the musical note c which is in the middle of the piano keyboard.
answer:
middle c