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: a flashlight requires a source of electricity to produce light. 
Sentence2: Flashlights provide the safest emergency lighting source.

Output: flashlight


Input: Consider Input: Sentence1: Earthquakes cause massive damage. 
Sentence2: tectonic plates being pushed together causes massive damage.

Output: damage


Input: Consider Input: Sentence1: a windmill converts wind energy into electricity primarily by using mechanical energy. 
Sentence2: An electric field is created by voltage.


Output: electricity