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: Viruses are parasites of cells. 
Sentence2: Populations of viruses do not grow through division because they are parasites.

Ex Output:
are


Ex Input:
Sentence1: a circle graph can be used to display percents. 
Sentence2: pie charts are circle graphs.

Ex Output:
circle


Ex Input:
Sentence1: Sperm are deposited in the vagina during sexual intercourse. 
Sentence2: Male gametes are called sperm.

Ex Output:

Sperm