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: Mating is generally preceded by courtship. 
Sentence2: Mating is generally similar across species.

Ex Output:
Mating


Ex Input:
Sentence1: Many plants respond to the days growing shorter in the fall by going dormant. 
Sentence2: Many plants respond to the autumnal equinox by going dormant.

Ex Output:
Many


Ex Input:
Sentence1: Gene flow occurs when individuals move into or out of a population. 
Sentence2: Genetic diversity can be maintained in small populations by even a small amount of gene flow.

Ex Output:

Gene