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: creating paper requires cutting down trees. 
Sentence2: Trees begin as epiphytes on host trees.

Output: trees


Input: Consider Input: Sentence1: Fertilization is the penetration of the egg by a sperm. 
Sentence2: Sperm must swim from the male to the female egg.

Output: egg


Input: Consider Input: Sentence1: folding an object causes that object to change shape. 
Sentence2: Tri-fold cards fold into three sections.


Output: folding