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: protein is used to repair cells by the human body. 
Sentence2: Wound healing requires protein.

Ex Output:
protein


Ex Input:
Sentence1: Smoking accelerates the aging process. 
Sentence2: smoking accelerates the death of cells.

Ex Output:
Smoking


Ex Input:
Sentence1: Weight lifting is an example of anaerobic exercise. 
Sentence2: weight lifting increases strength.

Ex Output:

Weight