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: Refrigerators are major users of electricity. 
Sentence2: Keeping food fresh for a long period of time requires a lot of electricity.

Output: electricity


Input: Consider Input: Sentence1: triceps contracting causes a person 's elbow to straighten. 
Sentence2: muscles contracting cause a person's elbow to straighten.

Output: contracting


Input: Consider Input: Sentence1: Many corals secrete an exoskeleton that builds up to become a coral reef. 
Sentence2: Many corals secrete a hard outer covering that builds up to become a coral reef.


Output: Many