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: creating wood-free paper does not require cutting down trees. 
Sentence2: creating printed media requires cutting down trees.

Ex Output:
creating


Ex Input:
Sentence1: the uterus is used in reproduction. 
Sentence2: Reproduction uses the same organ as menstruation.

Ex Output:
reproduction


Ex Input:
Sentence1: Some herbivores have more than one stomach. 
Sentence2: cows can be herbivores.

Ex Output:

herbivores