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.

Q: vichy is a "commune" in central france, in the auvergne-rhône-alpes region, along the allier river.

A: vichy
****
Q: aaron downey (born august 27, 1974 in shelburne, ontario) is a canadian retired professional ice hockey right winger that played 10 seasons in national hockey league.

A: aaron downey
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Q: a green roof or living roof is a roof of a building that is partially or totally covered with plants.

A:
green roof
****