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: an animal requires air for survival. 
Sentence2: It is breathed in by animals and restored to the air by the photosynthesis mechanism of plants.

Output: air


Input: Consider Input: Sentence1: Algae have varied life cycles. 
Sentence2: And fish eat algae.

Output: Algae


Input: Consider Input: Sentence1: heating salt water causes the water to evaporate while the salt remains. 
Sentence2: Evaporation of the water leaves the salt on the surface.


Output: evaporate


