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: Human mating behavior also involves some competition. 
Sentence2: Human mating may lead to aggressive behaviors or displays of aggresion.

Output: Human


Input: Consider Input: Sentence1: the moon revolving around the Earth causes the phases of the moon. 
Sentence2: Lets start our discussion of the Moon's phases with the New Moon phase.

Output: phases


Input: Consider Input: Sentence1: mountains are formed by earthquakes. 
Sentence2: Mountains are formed by moving plates.


Output: are