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: Results can be damaging or disastrous. 
Sentence2: Lack of immunization can be damaging or disastrous.

Ex Output:
damaging


Ex Input:
Sentence1: Adult echinoderms have radial symmetry. 
Sentence2: All animals with radial symmetry live in water.

Ex Output:

radial