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: Osteoporosis is a disease characterized by a decrease in bone mineral density. 
Sentence2: a disease in which osteoclasts are more active than osteoblasts results in a decrease in bone mineral density.

Output: bone


Input: Consider Input: Sentence1: Tree-ring dating the 1700 Cascadia earthquake. 
Sentence2: estimating the age of trees can be used in reviewing earthquake history.

Output: earthquake


Input: Consider Input: Sentence1: a fire requires oxygen to burn. 
Sentence2: A fire requires something with exactly eight protons to burn.


Output: burn