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.

Input: Consider Input: Sentence1: skin is used for protecting the body from harmful substances. 
Sentence2: Acids are harmful to tissue.

Output: harmful


Input: Consider Input: Sentence1: All sharks are predators. 
Sentence2: hiding can be used for avoiding sharks.

Output: sharks


Input: Consider Input: Sentence1: increasing heat causes thermal expansion. 
Sentence2: expansion can cause fatigue.


Output: expansion