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: wind is used for producing electricity. 
Sentence2: Wind is caused because of pressure differences in the atmosphere.

Output: wind


Input: Consider Input: Sentence1: propulsion is used for flying by a spacecraft. 
Sentence2: Jets are used for flying by spacecraft.

Output: flying


Input: Consider Input: Sentence1: Constriction occurs when the muscular walls of blood vessels contract. 
Sentence2: caffeine causes blood vessels to contract.


Output: contract