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: Leeches are external parasites. 
Sentence2: Leeches live on the surface of their hosts.

Ex Output:
Leeches


Ex Input:
Sentence1: electric devices require electrical energy to function. 
Sentence2: Lie detectors are electrical or mechanical devices.

Ex Output:
devices


Ex Input:
Sentence1: Population density is the average number of individuals per unit of area or volume. 
Sentence2: Growth of an area can be determined by the average number of people per unit of area.

Ex Output:

area