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.

Input: Consider Input: Sentence1: An accounting period is simply a period of time. 
Sentence2: seconds are used to measure a period.

Output: period


Input: Consider Input: Sentence1: Most soil nutrients are cations. 
Sentence2: decomposition increases the amount of cations in the soil.

Output: cations


Input: Consider Input: Sentence1: electricity sometimes is used for heating buildings. 
Sentence2: Sometimes, in a cold climate it is necessary to use heat, but use only slow heat.


Output: heating