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: an animal requires air for survival. 
Sentence2: It is breathed in by animals and restored to the air by the photosynthesis mechanism of plants.

Ex Output:
air


Ex Input:
Sentence1: healing requires rest. 
Sentence2: Healing and cell regeneration follows.

Ex Output:
healing


Ex Input:
Sentence1: DNA replication is the process in which DNA is copied. 
Sentence2: the process in which DNA is copied is necessary for cell division.

Ex Output:

DNA