import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.TreeMap;
import java.util.TreeSet;

public class Main {
	public static void main(String[] args) throws Exception {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		int n = Integer.parseInt(br.readLine());
		String[] sa = br.readLine().split(" ");
		int[] a = new int[n];
		for (int i = 0; i < n; i++) {
			a[i] = Integer.parseInt(sa[i]);
		}
		br.close();

		TreeMap<Integer, Integer> map = new TreeMap<>();
		for (int i = 0; i < n; i++) {
			map.put(a[i], i);
		}

		TreeSet<Integer> set = new TreeSet<>();
		boolean h = false;
		for (Integer k : map.keySet()) {
			if (set.size() == 0) {
			} else if (set.size() == 1) {
				if (set.last() < map.get(k)) {
					h = true;
				}
			} else {
				if (h && set.last() > map.get(k)) {
					int v1 = a[set.pollFirst()];
					int v2 = a[map.get(k)];
					int v3 = a[set.higher(map.get(k))];
					System.out.println(v1 + v2 + v3);
					return;
				}
				if (!h && set.first() < map.get(k)) {
					int v1 = a[set.pollLast()];
					int v2 = a[map.get(k)];
					int v3 = a[set.lower(map.get(k))];
					System.out.println(v1 + v2 + v3);
					return;
				}
			}
			set.add(map.get(k));
		}
		System.out.println(-1);
	}
}