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: propulsion is used for flying by a spacecraft. 
Sentence2: Jets are used for flying by spacecraft.

Output: flying


Input: Consider Input: Sentence1: when a hurricane moves over land , that hurricane will decrease in strength. 
Sentence2: Hurricanes form over the warm tropical water in ocean and die down when they move over land.

Output: land


Input: Consider Input: Sentence1: boiling is when liquids are heated above their boiling point. 
Sentence2: Lots of gas bubbles burst over the boiling lakes' surface.


Output: boiling