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: Basically, heat is energy. 
Sentence2: Head hair is especially important in preventing energy loss from the body.

Ex Output:
energy


Ex Input:
Sentence1: Frogs, toads and salamanders are amphibians. 
Sentence2: Salamanders have a relatively complex circulatory system with a three-chambered heart.

Ex Output:

salamanders