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: pathogens can cause disease. 
Sentence2: pathogens affects the immune system.

Ex Output:
pathogens


Ex Input:
Sentence1: wind is used for producing electricity. 
Sentence2: Winds are caused by pressure differences.

Ex Output:
wind


Ex Input:
Sentence1: Fertilization stimulates the growth of plankton algae. 
Sentence2: Fertilization helps feed bivalves.

Ex Output:

Fertilization