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.

Input: Consider Input: kappa (uppercase/lowercase ), is the letter of the greek alphabet, used to represent the "k" sound in ancient and modern greek.

Output: kappa

Input: Consider Input: a sandwich panel is a kind of composite material, which is usually made of two components: a small outside layer (which is the same on both sides), and an inside layer, which is used to get certain properties, for example insulation or fire resistance.

Output: sandwich panel

Input: Consider Input: the fuball-club gelsenkirchen-schalke 04, commonly known as fc schalke 04, is a successful and popular german football club.
Output: fc schalke 04