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: Apollo 13 spacecraft is launched. 
Sentence2: Propulsion was used for flying Apollo 13.

Ex Output:
13


Ex Input:
Sentence1: Interstellar space contains a plasma. 
Sentence2: interstellar space contains electrons, atoms, and stars.

Ex Output:
Interstellar


Ex Input:
Sentence1: smoking tobacco decreases stamina. 
Sentence2: Tobacco is smoked in pipes or in cigarettes or bidis.

Ex Output:

smoking