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: igneous rocks are formed from magma cooling. 
Sentence2: magma solidifies into igneous rocks.

Output: magma


Input: Consider Input: Sentence1: Any antigen that causes an allergy is called an allergen. 
Sentence2: Antigens are proteins foreign to the body.

Output: antigen


Input: Consider Input: Sentence1: the sun causes water to evaporate more quickly by adding heat. 
Sentence2: During the summer the sun gets much higher and provides more direct, concentrated heating.


Output: heat