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: Balance is the ability to sense and maintain body position. 
Sentence2: Another part of the inner ear is used for balance.

Ex Output:
Balance


Ex Input:
Sentence1: a plant requires sunlight to grow. 
Sentence2: Grass needs air and sunlight.

Ex Output:
sunlight


Ex Input:
Sentence1: Scientists still know relatively little about Archaea. 
Sentence2: some prokaryotes are little known by scientists.

Ex Output:

know