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: measurement unit 
Words: ounce, foot, kilometer, milimeter, heel
Example Output: heel

Example Input: Category: social gathering 
Words: group, clan, team, club, doorstep
Example Output: doorstep

Example Input: Category: animal 
Words: grasshopper, swim, pounce, drive, fly
Example Output:
drive