Generate an overlapping word between the given two sentences. When you find the overlapping words, they don't have to match exactly, e.g., "survival" and "survive" are valid overlapping words. Little words like "the" or "of" don't count! You must generate significant words which are not the stop words.

Input: Consider Input: Sentence1: Fish are the first known true chordates. 
Sentence2: Fish are the first known animal with a backbone.

Output: Fish


Input: Consider Input: Sentence1: a fire requires oxygen to burn. 
Sentence2: If the oxygen is removed, the fire is smothered.

Output: oxygen


Input: Consider Input: Sentence1: Smog also contains particulates. 
Sentence2: Aerosol is a collection of particulates.


Output: particulates