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: Protein Protein is needed for tissue maintenance and repair. 
Sentence2: protein repairs cells.

Ex Output:
Protein


Ex Input:
Sentence1: Energy is the fuel for chemical reactions which run the various systems of the body. 
Sentence2: running requires fuel for chemical reactions which run the various systems of the body.

Ex Output:
body


Ex Input:
Sentence1: Reptiles are a class of tetrapod vertebrates that produce amniotic eggs. 
Sentence2: Snakes are cold-blooded reptiles.

Ex Output:

Reptiles