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: when a gas in an open container evaporates , that gas spreads out into the air. 
Sentence2: when a gas in an open container evaporates gas molecules slamming into one another.

Ex Output:
container


Ex Input:
Sentence1: a circle graph can be used to display percents. 
Sentence2: pie charts are circle graphs.

Ex Output:
circle


Ex Input:
Sentence1: carbon dioxide concentrations in the air have increased over the last decade dramatically. 
Sentence2: Carbon dioxide is formed by burning carbon.

Ex Output:

dioxide