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.

Ex Input:
Sentence1: Coral Reefs Coral reefs are widely distributed in warm shallow waters. 
Sentence2: warm shallow waters provide food and shelter to many ocean organisms.

Ex Output:
shallow


Ex Input:
Sentence1: keeping food cold is used for keeping food fresh. 
Sentence2: Keeping food at 40 degrees F or lower is used for keeping food fresh.

Ex Output:
food


Ex Input:
Sentence1: astronauts require preserved food for extended flights. 
Sentence2: Most of the Shuttle foods are preserved by dehydration, which saves weight and storage space.

Ex Output:

preserved