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: Hydrogen bonds cause water to expand when it freezes. 
Sentence2: Hydrogen bonds Hydrogen bonds are primarily electrostatic in origin.

Ex Output:
Hydrogen


Ex Input:
Sentence1: Cells are the units of function in living things. 
Sentence2: living things cannot survive without oxygen.

Ex Output:
living


Ex Input:
Sentence1: pathogens can cause disease. 
Sentence2: Bacteria can cause disease.

Ex Output:

can