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.

Input: Consider Input: Sentence1: a warm front causes cloudy and rainy weather. 
Sentence2: Stratus clouds are associated with a warm front.

Output: front


Input: Consider Input: Sentence1: Every photograph is produced by a camera. 
Sentence2: Photographers record images.

Output: photograph


Input: Consider Input: Sentence1: Warm blooded animals have a constant body temperature. 
Sentence2: an animal usually requires constant body temperature for survival.


Output: constant