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: lightning can cause a forest fire. 
Sentence2: Lightning can cause a natural cycle in forests.

Output: lightning


Input: Consider Input: Sentence1: Some mollusks are nearly microscopic. 
Sentence2: Some squids are nearly microscopic.

Output: Some


Input: Consider Input: Sentence1: faulting of rock in Earth 's crust causes earthquakes. 
Sentence2: Earthquake tremors also frequently shatter window glass miles from the epicenter.


Output: earthquakes