Given a category and a set of five words, find the word from the set that does not belong (i.e. is the least relevant) with the other words in the category. Words are separated by commas.

Example Input: Category: physical property 
Words: thin, brittleness, heavy, angular momentum, fat
Example Output: heavy

Example Input: Category: animal 
Words: bus, leap, spider, run, fly
Example Output: bus

Example Input: Category: secretary duty 
Words: sort mail, reception, errands, space, file
Example Output:
space