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: mountains are formed by earthquakes. 
Sentence2: Mountains are formed by moving plates.

Output: are


Input: Consider Input: Sentence1: Mammalian teeth are important for digestion. 
Sentence2: bats' teeth are important for digestion.

Output: digestion


Input: Consider Input: Sentence1: competition may cause animals to fight towards members of their own species. 
Sentence2: Competition Animals compete for food and shelter.


Output: competition