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: Silica sand is primarily mined from sandstone deposits. 
Sentence2: erosion forms silica sand.

Ex Output:
Silica


Ex Input:
Sentence1: when electricity flows to a light bulb , the light bulb will turn on. 
Sentence2: water pumps can turn on light bulbs.

Ex Output:
bulb


Ex Input:
Sentence1: Biodiversity generally increases from the poles to the equator. 
Sentence2: Biodiversity contributes to ecosystem complexity.

Ex Output:

Biodiversity