In this task, you need to write a topic word from the given fact. The topic word must have at least one word overlap with the given fact. The topic word often involves adding a new word from a related concept. In your topic word, use at least one word from the given fact. Topic words with two or more words work best.

Ex Input:
Fact: a sifter is used for separating mixtures.

Ex Output:
Sifter.


Ex Input:
Fact: if a neutral atom loses an electron then an atom with a negative charge will be formed.

Ex Output:
atom electron.


Ex Input:
Fact: the number of rings in a tree trunk can be used to estimate the age of the tree.

Ex Output:

age of tree forest ring.