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: dew is formed when water vapor condenses over night. 
Sentence2: dew is formed when cooling  over night.

Output: dew


Input: Consider Input: Sentence1: erosion causes a river to become deeper and wider. 
Sentence2: On the contrary, the NILE is the longest river in Africa.

Output: river


Input: Consider Input: Sentence1: Biological structures are too complex. 
Sentence2: Cells are complex but all share basic functions.


Output: complex