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.

Input: Consider Input: Sentence1: keeping food cold is used for keeping food fresh. 
Sentence2: Keeping food cold is used to keep food simple and natural as possible.

Output: cold


Input: Consider Input: Sentence1: when a gas in an open container evaporates , that gas spreads out into the air. 
Sentence2: If you place gas in an open box it will evaporate and spread out into the air.

Output: gas


Input: Consider Input: Sentence1: bacteria in soil convert atmospheric nitrogen into a form usable by plants. 
Sentence2: Bacteria are single-celled organisms.


Output: bacteria