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: All oaks are trees. 
Sentence2: Cutting down oaks has a negative impact on an ecosystem.

Output: oaks


Input: Consider Input: Sentence1: Some herbivores have more than one stomach. 
Sentence2: Camels are an herbivore.

Output: herbivores


Input: Consider Input: Sentence1: when a river floods , that river deposits soil in flood plains. 
Sentence2: Examples of such streams are the Nile and Colorado Rivers.


Output: river