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: erosion of soil has a negative impact on the environment. 
Sentence2: erosion of soil has a negative impact on forests.

Ex Output:
erosion


Ex Input:
Sentence1: All cells share some of the same structures and basic functions. 
Sentence2: Biological structures are too complex.

Ex Output:

structures