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: ultraviolet light causes sunburn. 
Sentence2: Sunburn risk is higher at elevation.

Ex Output:
sunburn


Ex Input:
Sentence1: a flashlight converts chemical energy into light energy. 
Sentence2: Chemical energy converted to light energy requires batteries.

Ex Output:
chemical


Ex Input:
Sentence1: All lizards are reptiles. 
Sentence2: Lizards are tetrapod vertebrates that produce amniotic eggs.

Ex Output:

lizards