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.

Ex Input:
Sentence1: Nonmetal elements are far fewer in number. 
Sentence2: There are 17 nonmetals on the periodic table.

Ex Output:
Nonmetal


Ex Input:
Sentence1: Chemical weathering is the chemical disintigration of rocks. 
Sentence2: moss causes the chemical disintigration of rocks.

Ex Output:
chemical


Ex Input:
Sentence1: operating an automobile usually requires fossil fuels. 
Sentence2: Operating an automobile requires oil and gasoline.

Ex Output:

an