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

Ex Output:
sharks


Ex Input:
Sentence1: Mammals that are viviparous are called therian mammals. 
Sentence2: Mouse-sized viviparous mammals evolved by Jurassic times.

Ex Output:
Mammals


Ex Input:
Sentence1: a wildfire changes an ecosystem drastically. 
Sentence2: a wildfire changes a forest drastically.

Ex Output:

changes