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: Ions are atoms or groups of atoms that carry a positive or negative electrical charge. 
Sentence2: An ion is formed after a neutral atom loses an electron.

Ex Output:
Ions


Ex Input:
Sentence1: Heterotrophs get food by eating other living things. 
Sentence2: fish eat other living things.

Ex Output:
living


Ex Input:
Sentence1: Increases in carbon dioxide make the greenhouse effect worse. 
Sentence2: The greenhouse effect in the air  has become worse over the last decade.

Ex Output:

effect