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: cell division often causes growth. 
Sentence2: Mitosis is cell division.

Output: cell


Input: Consider Input: Sentence1: high pressure systems cause clear weather. 
Sentence2: Weather Clear weather usually means good visibility.

Output: clear


Input: Consider Input: Sentence1: gases from burning coal and oil dissolving in water in the atmosphere causes acid rain. 
Sentence2: A compound which can donate a proton from burning coal and oil dissolving in water in the atmosphere causes a compound which can donate a proton rain.


Output: atmosphere