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: Humans have collected and grown mushrooms for food for thousands of years. 
Sentence2: Yeast and mushrooms are types of fungus.

Ex Output:
mushrooms


Ex Input:
Sentence1: friction is used for stopping a vehicle by brakes. 
Sentence2: friction is used for stopping a car by brakes.

Ex Output:
brakes


Ex Input:
Sentence1: a laser is used for producing light. 
Sentence2: Lasers are an incredibly-powerful research tool.

Ex Output:

laser