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: riding a bike does not cause pollution. 
Sentence2: riding a bike does not release particles.

Output: bike


Input: Consider Input: Sentence1: a warm front causes cloudy and rainy weather. 
Sentence2: Cloudy, cool, or rainy weather can cause some algae scums to die.


Output: cloudy