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: when a river floods , that river deposits soil in flood plains. 
Sentence2: Hurricanes can cause local flooding, flash flooding, or coastal flooding.

Ex Output:
flood


Ex Input:
Sentence1: Muscles can only contract. 
Sentence2: Contraction is a type of movement.

Ex Output:
contract


Ex Input:
Sentence1: Reproduction is the process by which organisms give rise to offspring. 
Sentence2: Darwin's theory of evolution depends on more offspring than are needed to maintain the species.

Ex Output:

offspring