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.

Input: Consider Input: Sentence1: cold fronts cause thunderstorms as they pass by. 
Sentence2: Cold fronts cause lightning.

Output: cold


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

Output: burn


Input: Consider Input: Sentence1: Climate is generally described in terms of temperature and moisture. 
Sentence2: temperature and moisture varies by alltitude.


Output: moisture