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: Trees have woody stems covered with bark. 
Sentence2: Evergreens have woody stems covered with bark.

Output: bark


Input: Consider Input: Sentence1: If there is sun, there is sunlight, there is day. 
Sentence2: Energy enters ecosystems from the sun.

Output: sun


Input: Consider Input: Sentence1: Leaves help carry on photosynthesis. 
Sentence2: as a plant grows, photosynthesis increases.


Output: photosynthesis