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: a flashlight converts chemical energy into light energy. 
Sentence2: Only as long as there are batteries in the flashlight, the flashlight will function.

Ex Output:
flashlight


Ex Input:
Sentence1: All sharks are predators. 
Sentence2: hiding can be used for avoiding sharks.

Ex Output:
sharks


Ex Input:
Sentence1: the emission of sulfur dioxide causes acid rain. 
Sentence2: Acid rain is killing our forests and our fish.

Ex Output:

acid