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: waxy leaves are used for storing water by some plants. 
Sentence2: waxy leaves are used for water conservation by some plants.

Ex Output:
leaves


Ex Input:
Sentence1: Basically, heat is energy. 
Sentence2: Head hair is especially important in preventing energy loss from the body.

Ex Output:
energy


Ex Input:
Sentence1: Streams and rivers are crossed on rocks, beaver dams, on fallen trees or by wading. 
Sentence2: Hydropower requires beavers damming streams with fallen trees.

Ex Output:

Streams