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: Examples of gametes are ova and spermatozoa. 
Sentence2: fertilization of ova and spermatozoa produces a diploid zygote.

Ex Output:
ova


Ex Input:
Sentence1: Ozone depletion results in higher levels of UV radiation reaching Earth. 
Sentence2: less ozone means more ultraviolet light.

Ex Output:
Ozone


Ex Input:
Sentence1: Light energy is converted into heat energy. 
Sentence2: electrical energy  is converted into heat energy.

Ex Output:

converted