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: First, the bottle is calibrated with a graduated cylinder. 
Sentence2: calibration is performed with a cylinder.

Ex Output:
calibrated


Ex Input:
Sentence1: a fire requires oxygen to burn. 
Sentence2: A fire requires something with exactly eight protons to burn.

Ex Output:
burn


Ex Input:
Sentence1: Carbon monoxide is a gas produced by furnaces and other devices that burn fuel. 
Sentence2: Carbon Monoxide Carbon monoxide is a health hazard.

Ex Output:

Carbon