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: Flies are insects with two wings. 
Sentence2: Flies are arthropods with two wings.

Ex Output:
Flies


Ex Input:
Sentence1: Osteoporosis is a disease in which osteoclasts are more active than osteoblasts. 
Sentence2: a thinning and weakening of bone is a disease in which osteoclasts are more active than osteoblasts.

Ex Output:
active


Ex Input:
Sentence1: RNA polymerase joins the RNA nucleotides together. 
Sentence2: DNA contains genetic instructions for proteins where polymerase joins the nucleotides together.

Ex Output:

joins