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: All oaks are trees. 
Sentence2: Cutting down oaks has a negative impact on an ecosystem.

Ex Output:
oaks


Ex Input:
Sentence1: Smoking accelerates the aging process. 
Sentence2: smoking accelerates the death of cells.

Ex Output:
Smoking


Ex Input:
Sentence1: Rulers are divided into inches and fractions of inches. 
Sentence2: You can measure the length of an object with inches and fractions of inches.

Ex Output:

fractions