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

Output: sun


Input: Consider Input: Sentence1: a breathing mask is used for keeping harmful particles from entering the respiratory system. 
Sentence2: Another respiratory defense is the immune system.


Output: respiratory