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: Plants use unsaturated fatty acids to store energy. 
Sentence2: Plants and fish contain fatty acids.

Ex Output:
Plants


Ex Input:
Sentence1: friction causes the temperature of an object to increase. 
Sentence2: internal combustion engines get hot.

Ex Output:
temperature


Ex Input:
Sentence1: stalactites are formed by deposition. 
Sentence2: cave roofs are formed by deposition.

Ex Output:

deposition