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: harming an animal species has a negative impact on the population size of that species. 
Sentence2: the rarity of a species increases harm to population exponentially.

Ex Output:
harming


Ex Input:
Sentence1: Sand and mud are examples of sediments. 
Sentence2: layers of sand over the remains of organisms over time can create fossils.

Ex Output:
Sand


Ex Input:
Sentence1: Most cells are too small to be seen without a microscope. 
Sentence2: Cells vary in size as well as shape and are seen with a microscope.

Ex Output:

microscope


