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: skin is used for protecting the body from harmful substances. 
Sentence2: Acids are harmful to tissue.

Ex Output:
harmful


Ex Input:
Sentence1: friction causes the temperature of an object to increase. 
Sentence2: When we increase the temperature of objects, they always expand.

Ex Output:
increase


Ex Input:
Sentence1: a thermometer is used to measure temperature. 
Sentence2: Heat and temperature are the same.

Ex Output:

temperature