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: Heterotrophs are living things that cannot make their own food. 
Sentence2: food contains organic molecules.

Output: food


Input: Consider Input: Sentence1: Ice is frozen water. 
Sentence2: ice expands.

Output: Ice


Input: Consider Input: Sentence1: Light is the visible form of electromagnetic energy. 
Sentence2: A mirror is used for reflecting visible energy.


Output: energy