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: Endospores are commonly found in soil and water. 
Sentence2: Some bacteria form resistant cells called endospores.

Ex Output:
Endospores


Ex Input:
Sentence1: travelling requires navigation. 
Sentence2: travelling requires a bit a of getting used to.

Ex Output:

travelling