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: Ice is frozen water. 
Sentence2: ice expands.

Ex Output:
Ice


Ex Input:
Sentence1: Telephone Telephone calls are expensive. 
Sentence2: Communicating by transmitting sound is expensive.

Ex Output:
expensive


Ex Input:
Sentence1: Heat is emitted energy. 
Sentence2: Mammals conserve body energy with their hair or fur.

Ex Output:

energy