import java.util.Scanner; import java.util.Set; import java.util.TreeSet; /** * Created by dean on 2017/4/27. */ public class Main { public static void main(String[] args) { Scanner scan = new Scanner(System.in); int n = scan.nextInt(); Set<Integer> set = new TreeSet<>(); for (int i = 0; i < n; ++i) { set.add(scan.nextInt()); } int p = 0; for (int num : set) { p++; if (p == 3) { System.out.println(num); break; } } if (p < 3){ System.out.println(-1); } } }