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: friction causes the temperature of an object to increase. 
Sentence2: Friction causes the temperature of a toy to increase.

Ex Output:
causes


Ex Input:
Sentence1: DNA is made up of nucleotides. 
Sentence2: Mutations can change the structure of DNA.

Ex Output:
DNA


Ex Input:
Sentence1: coal is used to produce electricity by burning in coal-fire power stations. 
Sentence2: coal is a bargain.

Ex Output:

coal