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: Ferns are vascular plants. 
Sentence2: when a fern grows, its size of leaves may increase.

Output: Ferns


Input: Consider Input: Sentence1: Enzymes are chemicals involved in digestion. 
Sentence2: Enzymes involved in digestion occur mainly in the small intestine.


Output: Enzymes