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: Secondary accidents are a major problem under driving conditions of reduced visibility.
Sentence2: Bad weather increases the risk of car accidents.

Output: Secondary

Input: Consider Input: Sentence1: Streams may start with runoff or water seeping out of a spring.
Sentence2: streams may start with runoff or h2o seeping out of a spring.

Output: Streams

Input: Consider Input: Sentence1: gases from burning coal and oil dissolving in water in the atmosphere causes acid rain.
Sentence2: A compound which can donate a proton from burning coal and oil dissolving in water in the atmosphere causes a compound which can donate a proton rain.
Output: atmosphere