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: cold fronts cause thunderstorms as they pass by. 
Sentence2: Thunderstorms create havoc.

Ex Output:
thunderstorms


Ex Input:
Sentence1: Mammals depend on the vegetation for food and shelter. 
Sentence2: Mammals are Heterotrophs.

Ex Output:
Mammals


Ex Input:
Sentence1: when the seasons change from the summer to the fall , the amount of daylight will decrease. 
Sentence2: in fall the days become colder.

Ex Output:

fall