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: An accounting period is simply a period of time. 
Sentence2: seconds are used to measure a period.

Ex Output:
period


Ex Input:
Sentence1: Specialization decreases mortality 12,13 and increases survival. 
Sentence2: evolving different adaptations increases survival.

Ex Output:
increases


Ex Input:
Sentence1: heating salt water causes the water to evaporate while the salt remains. 
Sentence2: On high heat, bring to a boil.

Ex Output:

heating