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: Acid rain is precipitation which pH is 5.7 or lower. 
Sentence2: gases from burning coal causes precipitation which pH is 5.7 or lower.

Output: 5


Input: Consider Input: Sentence1: Angiosperm sporophyte is dominant. 
Sentence2: Flowers form on angiosperms.

Output: Angiosperm


Input: Consider Input: Sentence1: darkness has a negative impact on photosynthesis. 
Sentence2: Darkness has a negative impact on plant growth.


Output: darkness