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: Insects have 2 antennae. 
Sentence2: Insects have 2 appendages to detect sound.

Ex Output:
2


Ex Input:
Sentence1: Sound vibrations travel at different speeds through different materials. 
Sentence2: the type of material through which sound passes changes the sound vibrations.

Ex Output:
Sound


Ex Input:
Sentence1: smoking tobacco decreases stamina. 
Sentence2: Smoking cigarettes decreases stamina.

Ex Output:

decreases