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: If there is enough moisture in the clouds, rain is produced. 
Sentence2: Clouds lacking water reduces rainfall.

Ex Output:
clouds


Ex Input:
Sentence1: sharpening an object causes that object to change shape. 
Sentence2: sharpening a knife causes it to change shape.

Ex Output:
causes


Ex Input:
Sentence1: smoking tobacco decreases stamina. 
Sentence2: Good cigars or quality cigars contain only tobacco.

Ex Output:

tobacco