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: Producers use energy and inorganic molecules to make food. 
Sentence2: Green plants use energy and inorganic molecules to make food.

Ex Output:
energy


Ex Input:
Sentence1: Eggs are usually laid in a nest. 
Sentence2: birds have nests.

Ex Output:
nest


Ex Input:
Sentence1: plasma is formed by electrons separating from atoms in stars. 
Sentence2: Electrons separating from atoms in certain bright astronomical objects forms plasma.

Ex Output:

atoms