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: Ice is frozen water. 
Sentence2: ice expands.

Output: Ice


Input: Consider Input: Sentence1: lightning can cause a forest fire. 
Sentence2: Lightning can cause a natural cycle in forests.

Output: lightning


Input: Consider Input: Sentence1: Mangoes are propagated vegetatively and by seeds. 
Sentence2: animals propagate mangoes.


Output: Mangoes