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: Ions are atoms or groups of atoms that carry a positive or negative electrical charge. 
Sentence2: An ion is formed after a neutral atom loses an electron.

Ex Output:
Ions


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: Water helps to control the weather and climate. 
Sentence2: water is related to climate.

Ex Output:

Water