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: If the oxygen is removed, the fire is smothered.

Ex Output:
oxygen


Ex Input:
Sentence1: Fish are the first known true chordates. 
Sentence2: Fish are the first known animal with a backbone.

Ex Output:
Fish


Ex Input:
Sentence1: Communication Communication is exchange of Information. 
Sentence2: A radio is used for exchange of information.

Ex Output:

Information