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: Rivers, rainwater, well water and most lakes contain fresh water. 
Sentence2: canyons are formed by rainwater.

Ex Output:
rainwater


Ex Input:
Sentence1: Genetics is the study of inheritance. 
Sentence2: Pedigrees are useful tools for studying genetics.

Ex Output:
Genetics


Ex Input:
Sentence1: tidal energy can be used to produce electricity. 
Sentence2: spikes produce current.

Ex Output:

produce