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: wind is used for producing electricity. 
Sentence2: Winds are caused by pressure differences.

Ex Output:
wind


Ex Input:
Sentence1: Hydrogen bonds cause water to expand when it freezes. 
Sentence2: Hydrogen bonds Hydrogen bonds are primarily electrostatic in origin.

Ex Output:
Hydrogen


Ex Input:
Sentence1: carpooling decreases the amount of cars used to travel to a place. 
Sentence2: carpooling leads to less pollution.

Ex Output:

carpooling