using static System.Math;
using System;

public class Hello
{
    static void Main()
    {
        var n = int.Parse(Console.ReadLine().Trim());
        string[] line = Console.ReadLine().Trim().Split(' ');
        var a = Array.ConvertAll(line, int.Parse);
        var b = Array.ConvertAll(line, x => -int.Parse(x));
        var ans1 = getAns(n, a);
        var ans2 = getAns(n, b);
        int ans;
        if (ans1 == -1 && ans2 == -1) ans = -1;
        else if (ans1 == -1) ans = ans2;
        else if (ans2 == -1) ans = ans1;
        else ans = Min(ans1, -ans2);
        Console.WriteLine(ans);
    }
    static int getAns(int n, int[] a)
    {
        var bL = new int[n];
        var br = new int[n];
        bL[0] = a[0];
        br[n - 1] = a[n - 1];
        for (int i = 1; i < n; i++)
        {
            if (a[i] < bL[i - 1]) bL[i] = a[i];
            else bL[i] = bL[i - 1];
            if (a[n - 1 - i] < br[n - i]) br[n - 1 - i] = a[n - 1 - i];
            else br[n - 1 - i] = br[n - i];
        }
        var res = getAns1(n, a, bL, br);
        return res;
    }
    static int getAns1(int n, int[] a, int[] bL, int[] br)
    {
        var res = int.MaxValue;
        for (int i = 1; i < n - 1; i++)
        {
            if (a[i] > bL[i - 1] && a[i] > br[i + 1])
            {
                var t = a[i] + bL[i - 1] + br[i + 1];
                res = Min(res, t);
            }
        }
        if (res == int.MaxValue) return -1;
        else return res;
    }
}