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.

Input: Consider Input: Sentence1: a sifter is used for separating mixtures. 
Sentence2: a sifter is used for some recipes.

Output: sifter


Input: Consider Input: Sentence1: Acid rain is precipitation which pH is 5.7 or lower. 
Sentence2: gases from burning coal causes precipitation which pH is 5.7 or lower.

Output: 5


Input: Consider Input: Sentence1: the type of material through which sound passes changes the speed at which sound travels. 
Sentence2: Sound, a type of energy, is produced by vibrations and travels in waves.


Output: sound