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: wind is used for producing electricity. 
Sentence2: Wind is caused because of pressure differences in the atmosphere.

Ex Output:
wind


Ex Input:
Sentence1: Fertilization occurs naturally in the fallopian tubes. 
Sentence2: fertilization is used for reproduction.

Ex Output:
Fertilization


Ex Input:
Sentence1: magnetism can cause objects to repel each other. 
Sentence2: Electrical currents cause magnetic fields.

Ex Output:

magnetism