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: the mass of an object causes the gravitational force exerted by that object. 
Sentence2: gravitational force accelerates objects.

Output: force


Input: Consider Input: Sentence1: if an object is made of a material then that object has the properties of that material. 
Sentence2: If an object is made of a drug, then that object has the properties of that drug.

Output: made


Input: Consider Input: Sentence1: Gene flow tends to decrease differentiation. 
Sentence2: decreased differentiation tends to occur when individuals move into or out of a population.


Output: decrease