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: Some trees are maples. 
Sentence2: planting maples has a positive impact on an ecosystem.

Output: maples


Input: Consider Input: Sentence1: the mass of a planet causes the pull of gravity on that planet. 
Sentence2: the mass of a planet is what causes things to have weight.

Output: mass


Input: Consider Input: Sentence1: the gravitational pull of the Moon on Earth 's oceans causes the tides. 
Sentence2: gravitational pull of the moon causes waves.


Output: gravitational