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: employment activity 
Words: pay, instruct, heat, fire, scold
Example Output: heat

Example Input: Category: boats 
Words: hull, deck, rudder, check, lifeline
Example Output: check

Example Input: Category: emotional status 
Words: flat, down, emotional state, sad, unhappy
Example Output:
flat