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.

Ex Input:
Sentence1: Water is essential for all life on Earth. 
Sentence2: H2O is needed for all life on Eartth.

Ex Output:
Earth


Ex Input:
Sentence1: harming an animal species causes that animal 's population to decrease. 
Sentence2: Wild animal populations have decreased drastically, due to both hunting and loss of habitat.

Ex Output:
animal


Ex Input:
Sentence1: the emission of sulfur dioxide causes acid rain. 
Sentence2: emissions cause acid rain.

Ex Output:

emission