using System.Collections.Generic;
using static System.Math;
using System;

public class SB_BinarySearchTree<T> where T : IComparable
{
    public class Node
    {
        public T Value;
        public Node LChild;
        public Node RChild;
        public int Count;

        public Node(T v)
        {
            Value = v;
            Count = 1;
        }
    }

    static Random _rnd = new Random();

    public static int Count(Node t)
    {
        return t == null ? 0 : t.Count;
    }

    static Node Update(Node t)
    {
        t.Count = Count(t.LChild) + Count(t.RChild) + 1;
        return t;
    }

    public static Node Merge(Node l, Node r)
    {
        if (l == null || r == null) return l == null ? r : l;

        if (Count(l) / (double)(Count(l) + Count(r)) > _rnd.NextDouble())
        {
            l.RChild = Merge(l.RChild, r);
            return Update(l);
        }
        else
        {
            r.LChild = Merge(l, r.LChild);
            return Update(r);
        }
    }

    public static Tuple<Node, Node> Split(Node t, int k)
    {
        if (t == null) return new Tuple<Node, Node>(null, null);
        if (k <= Count(t.LChild))
        {
            var s = Split(t.LChild, k);
            t.LChild = s.Item2;
            return new Tuple<Node, Node>(s.Item1, Update(t));
        }
        else
        {
            var s = Split(t.RChild, k - Count(t.LChild) - 1);
            t.RChild = s.Item1;
            return new Tuple<Node, Node>(Update(t), s.Item2);
        }
    }

    public static Node Remove(Node t, T v)
    {
        if (Find(t, v) == null) return t;
        return RemoveAt(t, LowerBound(t, v));
    }

    public static Node RemoveAt(Node t, int k)
    {
        var s = Split(t, k);
        var s2 = Split(s.Item2, 1);
        return Merge(s.Item1, s2.Item2);
    }

    public static bool Contains(Node t, T v)
    {
        return Find(t, v) != null;
    }

    public static Node Find(Node t, T v)
    {
        while (t != null)
        {
            var cmp = t.Value.CompareTo(v);
            if (cmp > 0) t = t.LChild;
            else if (cmp < 0) t = t.RChild;
            else break;
        }
        return t;
    }

    public static Node FindByIndex(Node t, int idx)
    {
        if (t == null) return null;

        var currentIdx = Count(t) - Count(t.RChild) - 1;
        while (t != null)
        {
            if (currentIdx == idx) return t;
            if (currentIdx > idx)
            {
                t = t.LChild;
                currentIdx -= (Count(t == null ? null : t.RChild) + 1);
            }
            else
            {
                t = t.RChild;
                currentIdx += (Count(t == null ? null : t.LChild) + 1);
            }
        }

        return null;
    }

    public static int UpperBound(Node t, T v)
    {
        var torg = t;
        if (t == null) return -1;

        var ret = int.MaxValue;
        var idx = Count(t) - Count(t.RChild) - 1;
        while (t != null)
        {
            var cmp = t.Value.CompareTo(v);

            if (cmp > 0)
            {
                ret = Min(ret, idx);
                t = t.LChild;
                idx -= (Count(t == null ? null : t.RChild) + 1);
            }
            else if (cmp <= 0)
            {
                t = t.RChild;
                idx += (Count(t == null ? null : t.LChild) + 1);
            }
        }
        return ret == int.MaxValue ? Count(torg) : ret;
    }

    public static int LowerBound(Node t, T v)
    {
        var torg = t;
        if (t == null) return -1;

        var idx = Count(t) - Count(t.RChild) - 1;
        var ret = int.MaxValue;
        while (t != null)
        {
            var cmp = t.Value.CompareTo(v);
            if (cmp >= 0)
            {
                if (cmp == 0) ret = Min(ret, idx);
                t = t.LChild;
                if (t == null) ret = Min(ret, idx);
                idx -= t == null ? 0 : (Count(t.RChild) + 1);
            }
            else if (cmp < 0)
            {
                t = t.RChild;
                idx += (Count(t == null ? null : t.LChild) + 1);
                if (t == null) return idx;
            }
        }
        return ret == int.MaxValue ? Count(torg) : ret;
    }

    public static Node Insert(Node t, T v)
    {
        var ub = LowerBound(t, v);
        return InsertByIdx(t, ub, v);
    }

    static Node InsertByIdx(Node t, int k, T v)
    {
        var s = Split(t, k);
        return Merge(Merge(s.Item1, new Node(v)), s.Item2);
    }

    public static IEnumerable<T> Enumerate(Node t)
    {
        var ret = new List<T>();
        Enumerate(t, ret);
        return ret;
    }

    static void Enumerate(Node t, List<T> ret)
    {
        if (t == null) return;
        Enumerate(t.LChild, ret);
        ret.Add(t.Value);
        Enumerate(t.RChild, ret);
    }
}

public class Set<T> where T : IComparable
{
    protected SB_BinarySearchTree<T>.Node _root;

    public T this[int idx] { get { return ElementAt(idx); } }

    public int Count()
    {
        return SB_BinarySearchTree<T>.Count(_root);
    }

    public virtual void Insert(T v)
    {
        if (_root == null) _root = new SB_BinarySearchTree<T>.Node(v);
        else
        {
            if (SB_BinarySearchTree<T>.Find(_root, v) != null) return;
            _root = SB_BinarySearchTree<T>.Insert(_root, v);
        }
    }

    public void Clear()
    {
        _root = null;
    }

    public void Remove(T v)
    {
        _root = SB_BinarySearchTree<T>.Remove(_root, v);
    }

    public bool Contains(T v)
    {
        return SB_BinarySearchTree<T>.Contains(_root, v);
    }

    public T ElementAt(int k)
    {
        var node = SB_BinarySearchTree<T>.FindByIndex(_root, k);
        if (node == null) throw new IndexOutOfRangeException();
        return node.Value;
    }

    public int Count(T v)
    {
        return SB_BinarySearchTree<T>.UpperBound(_root, v) - SB_BinarySearchTree<T>.LowerBound(_root, v);
    }

    public int LowerBound(T v)
    {
        return SB_BinarySearchTree<T>.LowerBound(_root, v);
    }

    public int UpperBound(T v)
    {
        return SB_BinarySearchTree<T>.UpperBound(_root, v);
    }

    public Tuple<int, int> EqualRange(T v)
    {
        if (!Contains(v)) return new Tuple<int, int>(-1, -1);
        return new Tuple<int, int>(SB_BinarySearchTree<T>.LowerBound(_root, v), SB_BinarySearchTree<T>.UpperBound(_root, v) - 1);
    }

    public List<T> ToList()
    {
        return new List<T>(SB_BinarySearchTree<T>.Enumerate(_root));
    }
}

public class MultiSet<T> : Set<T> where T : IComparable
{
    public override void Insert(T v)
    {
        if (_root == null) _root = new SB_BinarySearchTree<T>.Node(v);
        else _root = SB_BinarySearchTree<T>.Insert(_root, v);
    }
}

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 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 ans1 = getAns1(n, a, bL, br);
        var ans2 = getAns2(n, a);
        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 getAns2(int n, int[] a)
    {
        var ssL = new Set<int>();
        var ssr = new Set<int>();
        for (int i = 1; i < n; i++) ssr.Insert(a[i]);
        var res = int.MaxValue;
        for (int i = 1; i < n - 1; i++)
        {
            ssL.Insert(a[i - 1]);
            ssr.Remove(a[i]);
            var p = ssL.UpperBound(a[i]);
            var p2 = ssr.UpperBound(a[i]);
            if (p <= i - 1 && p2 <= n - 1 - i)
            {
                if (a[i] < ssL.ElementAt(p) && a[i] < ssr.ElementAt(p2))
                {
                    res = Min(res, a[i] + ssL.ElementAt(p) + ssr.ElementAt(p2));
                }
            }
        }
        if (res == int.MaxValue) return -1;
        else 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;
    }
}