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: Carbon cycles quickly between organisms and the atmosphere. 
Sentence2: the atmosphere is essential to all living organisms.

Ex Output:
organisms


Ex Input:
Sentence1: Weather today is said to be sunny and clear. 
Sentence2: High pressure systems cause it to be sunny.

Ex Output:
sunny


Ex Input:
Sentence1: Natural selection is differential reproduction. 
Sentence2: Behaviors that improve fitness increase through differential reproduction.

Ex Output:

differential


