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: Genetics is the study of inheritance. 
Sentence2: Pedigrees are useful tools for studying genetics.

Ex Output:
Genetics


Ex Input:
Sentence1: a light bulb is used for seeing in the dark. 
Sentence2: light is required for seeing.

Ex Output:
seeing


Ex Input:
Sentence1: increasing heat causes thermal expansion. 
Sentence2: Thermal burns are caused by exposure to heat.

Ex Output:

heat