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: Batteries are a better source of DC electricity. 
Sentence2: a flashlight requires batteries to produce light.

Ex Output:
Batteries


Ex Input:
Sentence1: Interstellar space contains a plasma. 
Sentence2: interstellar space contains electrons, atoms, and stars.

Ex Output:
Interstellar


Ex Input:
Sentence1: if an object is black then that object absorbs all visible light. 
Sentence2: Black holes emit no light.

Ex Output:

light