import java.util.NavigableSet;
import java.util.TreeSet;
public class CityNavigator {
static NavigableSet citiesSet;
public static void main(String[] args) {
String[] cities = { "A", "B", "C", "D", "E", "F" };
citiesSet = new TreeSet();
for (String city : cities)
citiesSet.add(city);
System.out.println(citiesSet.ceiling("A"));
}
}