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: Male dogs use pheromones in urine to mark their territory. 
Sentence2: Pheromones are hormones that are thought to stimulate, through smell, sexual reactions in animals.

Output: pheromones


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: an organism requires energy for growth. 
Sentence2: an organism requires food for growth.


Output: an