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: Bees feed on nectar and pollen. 
Sentence2: Plant reproduction often requires bees and nectar.

Ex Output:
Bees


Ex Input:
Sentence1: Heat and temperature are the same. 
Sentence2: a thermometer is used to measure heat.

Ex Output:
Heat


Ex Input:
Sentence1: An example of a cartilaginous fish is a shark. 
Sentence2: jaws make sharks excellent predators.

Ex Output:

shark