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: Energy enters ecosystems in the form of sunlight or chemical compounds. 
Sentence2: Energy enters ecosystems in the form of photons.

Output: Energy


Input: Consider Input: Sentence1: Light source is an ultra-bright, unbreakable LED Bulb. 
Sentence2: LEDs convert electricity into light and heat energy.

Output: LED


Input: Consider Input: Sentence1: Menopause occurs when menstruation stops occurring, usually in middle adulthood. 
Sentence2: Menstruation begins in puberty and ends with menopause .


Output: menstruation