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: Oxygen fatigue is a shortage of oxygen reaching the brain. 
Sentence2: Plants can reduce fatigue during the daytime.

Ex Output:
fatigue


Ex Input:
Sentence1: a thermometer is used to measure temperature. 
Sentence2: a thermometer is used to measure heat.

Ex Output:
a


Ex Input:
Sentence1: seeing requires light. 
Sentence2: Sight is the mere ability to see, and the eye's responses to light shining into it.

Ex Output:

seeing