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: Many corals secrete an exoskeleton that builds up to become a coral reef. 
Sentence2: Good examples are Bubble coral, Elegance coral, Frogspawn and other Euphyllia corals.

Ex Output:
coral


Ex Input:
Sentence1: Some trees are maples. 
Sentence2: planting maples has a positive impact on an ecosystem.

Ex Output:
maples


Ex Input:
Sentence1: Men seek the excitement of stimulants, because, for the time, the results are agreeable. 
Sentence2: Caffeine excites the central nervous system.

Ex Output:

excitement