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: a fire requires oxygen to burn. 
Sentence2: A fire requires something with exactly eight protons to burn.

Ex Output:
burn


Ex Input:
Sentence1: condensing causes a liquid to form. 
Sentence2: Air carries moisture that causes a liquid to form.

Ex Output:
causes


Ex Input:
Sentence1: a stove is used for cooking by generating heat. 
Sentence2: Wood stoves for cooking and heating.

Ex Output:

stove