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: Complex chemistry is needed to carry out all the functions of life. 
Sentence2: Chemistry is primarily concerned with matter, energy, and their interactions.

Output: chemistry


Input: Consider Input: Sentence1: Sperm had to swim from male to female reproductive organs for fertilization. 
Sentence2: If fertilized, the egg implants itself in the uterus.

Output: fertilization


Input: Consider Input: Sentence1: an animal usually requires a warm body temperature for survival. 
Sentence2: An animal usually requires a warm body heat measurement for survival?.


Output: a