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: natural magnetism is used for pointing north by a compass. 
Sentence2: For the ordinary compass, align to the North direction.

Output: north


Input: Consider Input: Sentence1: Molecules are the building blocks of a cell. 
Sentence2: molecules build cells.


Output: Molecules