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: Fish are the first known true chordates. 
Sentence2: Fish are the first known animal with a backbone.

Ex Output:
Fish


Ex Input:
Sentence1: a thermometer is used to measure temperature. 
Sentence2: a thermometer is used to measure heat.

Ex Output:
a


Ex Input:
Sentence1: Cell division is how organisms grow and repair themselves. 
Sentence2: Mitosis is how organisms grow and repair themselves.

Ex Output:

and