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: a tape measure is used to measure length. 
Sentence2: Length The Base unit for length in the metric system is the meter .

Ex Output:
length


Ex Input:
Sentence1: a flashlight converts chemical energy into light energy. 
Sentence2: Only as long as there are batteries in the flashlight, the flashlight will function.

Ex Output:
flashlight


Ex Input:
Sentence1: lightning can cause a forest fire. 
Sentence2: Static electricity is the cause of lightning.

Ex Output:

lightning