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

Output: evolution


Input: Consider Input: Sentence1: an animal requires warmth for survival. 
Sentence2: Light and heat and warmth are basic necessities for survival.

Output: warmth


Input: Consider Input: Sentence1: Many hormones are proteins . 
Sentence2: many chemical messengers that control body functions are proteins.


Output: proteins