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: If the skin is painful, seek medical attention. 
Sentence2: If your skin hurts, your touch receptors will sense differences.

Ex Output:
skin


Ex Input:
Sentence1: Rivers, rainwater, well water and most lakes contain fresh water. 
Sentence2: canyons are formed by rainwater.

Ex Output:
rainwater


Ex Input:
Sentence1: An insulator is the opposite of a conductor. 
Sentence2: Wiring requires the opposite of an insulator.

Ex Output:

insulator