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: Sperm had to swim from male to female reproductive organs for fertilization. 
Sentence2: If fertilized, the egg implants itself in the uterus.

Ex Output:
fertilization


Ex Input:
Sentence1: Somebody's got to decide which way to go, and both directions have possibilities. 
Sentence2: navigation requires knowing which way to go.

Ex Output:

go