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: Limestone caves displaying stalactites. 
Sentence2: Limestone caves are formed by depositions.

Output: Limestone


Input: Consider Input: Sentence1: Most copepods feed on phytoplankton. 
Sentence2: most copepods feed on bacteria and algae that use sunlight to make food.

Output: copepods


Input: Consider Input: Sentence1: Truth is the sound of one frog croaking. 
Sentence2: Frogs also have a larynx, or voice box, to croak.


Output: croaking