Generate a topic word for the given sentence. A topic word is usually the name of a person, place, animal, concept or object the sentence is focusing on.

Input: Consider Input: the alkaline earth metals are the second group of metals on the periodic table.

Output: alkaline earth metal


Input: Consider Input: vitoria-gasteiz is the basque country capital.

Output: vitoria-gasteiz


Input: Consider Input: ayalon river (, "nahal ayalon", "nahr el barideh" or wadi musrara, in arabic) is a river in central israel.


Output: ayalon river