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: conserving water can be used for survival in a dry environment. 
Sentence2: conserving water can be used for survival in deserts.

Ex Output:
conserving


Ex Input:
Sentence1: Soil Erosion Soil erosion is a natural process. 
Sentence2: wind and rain is a natural process.

Ex Output:
natural


Ex Input:
Sentence1: Any antigen that causes an allergy is called an allergen. 
Sentence2: Allergens can trigger asthma attacks.

Ex Output:

allergen