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: Mollusks are invertebrates such as the common snail. 
Sentence2: snails have no backbone.

Ex Output:
snail


Ex Input:
Sentence1: Most invertebrates have a nervous system. 
Sentence2: jellyfish have a nervous system.

Ex Output:

have