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.

Ex Input:
Sentence1: All monkeys are mammals. 
Sentence2: monkeys conserve body heat with their hair or fur.

Ex Output:
monkeys


Ex Input:
Sentence1: when electricity flows to a light bulb , the light bulb will turn on. 
Sentence2: water pumps can turn on light bulbs.

Ex Output:
bulb


Ex Input:
Sentence1: Water behind a dam has potential energy that can be converted to kinetic energy. 
Sentence2: a generator is used to turn water behind a dam into electrical energy.

Ex Output:

Water