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: a wildfire changes an ecosystem drastically. 
Sentence2: Forest fires change an ecosystem drastically.

Ex Output:
changes


Ex Input:
Sentence1: Chemical weathering is the chemical disintigration of rocks. 
Sentence2: moss causes the chemical disintigration of rocks.

Ex Output:
chemical


Ex Input:
Sentence1: exercise increases a body 's strength. 
Sentence2: Exercise is more than running and lifting.

Ex Output:

exercise