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: Cells are programmed to divide only a set number of times. 
Sentence2: Cells reproduce asexually, by dividing.

Output: divide


Input: Consider Input: Sentence1: lightning can cause a forest fire. 
Sentence2: Lightning can cause a natural cycle in forests.

Output: lightning


Input: Consider Input: Sentence1: Any antigen that causes an allergy is called an allergen. 
Sentence2: Many of the common allergens are pollens and dusts.


Output: allergen