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: Finally, the fluid in the nephron reaches a collecting duct . 
Sentence2: fluid in the kidneys collect into ducts.

Ex Output:
fluid


Ex Input:
Sentence1: Fertilization is the penetration of the egg by a sperm. 
Sentence2: Sperm must swim from the male to the female egg.

Ex Output:
egg


Ex Input:
Sentence1: Plants that shed their leaves seasonally each year are called deciduous plants. 
Sentence2: Grapevines shed their leaves seasonally each year.

Ex Output:

each