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: a solution is formed by one substance being dissolved in another substance. 
Sentence2: A solution is formed when limestone is dissolved in ocean water.

Ex Output:
formed


Ex Input:
Sentence1: An accounting period is simply a period of time. 
Sentence2: seconds are used to measure a period.

Ex Output:
period


Ex Input:
Sentence1: Currents flow across the large bodies of water from continent to continent. 
Sentence2: A ship is used to move people from continent to continent.

Ex Output:

continent