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: a warm front causes cloudy and rainy weather. 
Sentence2: Stratus clouds are associated with a warm front.

Ex Output:
front


Ex Input:
Sentence1: keeping food cold is used for keeping food fresh. 
Sentence2: Keeping food cold is used to keep food simple and natural as possible.

Ex Output:
cold


Ex Input:
Sentence1: Fertilization of gametes produces a diploid zygote. 
Sentence2: Diploid zygote forms multicellular embryo in venter.

Ex Output:

diploid