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 corruption perceptions index is an index that shows how corrupt certain countries are.
[EX A]: corruption perceptions index

[EX Q]: in cryptography, a pre-shared key or psk is a shared secret which was previously shared between the two parties using some secure channel before it is used.
[EX A]: pre-shared key

[EX Q]: mount kelut is a volcano in indonesia.
[EX A]:
kelut