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: Very often their only metal object in the house is a cooking pot or a knife. 
Sentence2: sharpening a knife causes it to change shape.

Ex Output:
knife


Ex Input:
Sentence1: Interest in fossils is worldwide. 
Sentence2: paleontologists study something with worldwide interest.

Ex Output:
Interest


Ex Input:
Sentence1: wind is used for producing electricity. 
Sentence2: wind can be used to produce heat.

Ex Output:

wind