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: DNA is made up of nucleotides. 
Sentence2: Mutations can change the structure of DNA.

Output: DNA


Input: Consider Input: Sentence1: Heat production is increased by shivering and non-shivering thermogenesis . 
Sentence2: Heat production occurs when many muscles contract a little bit all at once.

Output: Heat


Input: Consider Input: Sentence1: oil is formed by layers of sediment pushing down on decomposing algae. 
Sentence2: Oil can be formed by sediment pushing down on simple green plants.


Output: by