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: DNA is made up of nucleotides. 
Sentence2: Mutations can change the structure of DNA.

Ex Output:
DNA


Ex Input:
Sentence1: Mad Cow disease is a concern. 
Sentence2: pathogens can cause Mad Cow.

Ex Output:
Cow


Ex Input:
Sentence1: Contact with infected blood, contaminated needles. 
Sentence2: scraping oneself on an infected needle may cause infection.

Ex Output:

infected