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: Antigens are proteins foreign to the body. 
Sentence2: antigens are proteins.

Ex Output:
proteins


Ex Input:
Sentence1: Runoff water is wasted water. 
Sentence2: Streams may start with wasted water.

Ex Output:
wasted


Ex Input:
Sentence1: if soil is permeable then water easily flows through that soil. 
Sentence2: Permeability is affected by many soil characteristics.

Ex Output:

permeable