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: a solution is formed by one substance being dissolved in another substance. 
Sentence2: A solution is formed when limestone is dissolved in ocean water.

Output: formed


Input: Consider Input: Sentence1: Mutations are essential for evolution to occur. 
Sentence2: Genes are altered for evolution to occur.

Output: evolution


Input: Consider Input: Sentence1: Many corals secrete an exoskeleton that builds up to become a coral reef. 
Sentence2: many corals secrete an external framework that builds up to become a coral reef.


Output: Many