using System; using System.Collections.Generic; using System.Linq; using System.IO; using System.Text; using System.Numerics; using System.Threading; using System.Runtime.CompilerServices; using System.Diagnostics; using static System.Math; using static System.Array; using static AtCoder.Sc_out; using static AtCoder.Tool; using static AtCoder.ModInt; namespace AtCoder { class AC { //const int MOD = 1000000007; const int MOD = 998244353; const int INF = int.MaxValue / 2; const long SINF = long.MaxValue / 2; const double EPS = 1e-8; static readonly int[] dI = { 0, 1, 0, -1, 1, -1, -1, 1 }; static readonly int[] dJ = { 1, 0, -1, 0, 1, 1, -1, -1 }; //static List> G = new List>(); //static List> G = new List>(); //static List E = new List(); static void Main(string[] args) { var sw = new StreamWriter(Console.OpenStandardOutput()) { AutoFlush = false }; Console.SetOut(sw); var th = new Thread(Run, 1 << 26); th.Start(); th.Join(); //Run(); Console.Out.Flush(); } static void Run() { int Testcase = 1; for (var _ = 0; _ < Testcase; _++) Solve(); } static void Solve() { int N = Cin.Int; var seg_mx = new SegmentTree(N + 1, Max, -INF); var seg_mx2 = new SegmentTree(N + 1, Max, -INF); var A = Cin.ReadSplitInt; for (var i = 0; i < N; i++) A[i] = -A[i]; var sA = new (int, int)[N]; for (var i = 0; i < N; i++) sA[i] = (A[i], i); Sort(sA); var idx = new int[N]; for (var i = 0; i < N; i++) { idx[i] = sA[i].Item2; seg_mx.Assign(i, A[i]); } seg_mx.Set_All(); long ans = -SINF; for(var i = 1; i < N - 1; i++) { //B is min int max_l = seg_mx.Query_Answer(0, i); int max_r = seg_mx.Query_Answer(i + 1, N); //Out_Sep(max_l, max_r); if (max_l > A[i] && max_r > A[i]) ans = Max(ans, A[i] + max_r + max_l); } for(var i = 0; i < N; i++) { //B is max if (idx[i] == 0 || idx[i] == N - 1) { seg_mx2.Query_Update(idx[i], A[idx[i]]); continue; } int B = A[idx[i]]; int max_l = seg_mx2.Query_Answer(0, idx[i]); int max_r = seg_mx2.Query_Answer(idx[i] + 1, N); //Out_Sep(idx[i], max_l, max_r); if (max_l > 0 && max_r > 0) ans = Max(ans, B + max_l + max_r); seg_mx2.Query_Update(idx[i], A[idx[i]]); } OutL(ans == -SINF ? -1 : -ans); } public struct Edge { public int from; public int to; public long dist; public Edge(int t, long c) { from = -1; to = t; dist = c; } public Edge(int f, int t, long c) { from = f; to = t; dist = c; } } } public class SegmentTree { int n; T[] Tree; Func f; T ex; public SegmentTree(int size, Func fun, T exvalue) { f = fun; ex = exvalue; n = 1; while (n < size) n <<= 1; Tree = new T[(n << 1) - 1]; for (var i = 0; i < Tree.Length; i++) Tree[i] = ex; } public SegmentTree(int size, Func f, T exvalue, T initial) : this(size, f, exvalue) { for (var i = 0; i < size; i++) Tree[i + n - 1] = initial; Set_All(); } public void Set_All() { for (var i = n - 2; i >= 0; i--) { Tree[i] = f(Tree[(i << 1) + 1], Tree[(i << 1) + 2]); } } public void Assign(int ind, T val) { Tree[ind + n - 1] = val; } public void Update(int ind) { int i = ind + n - 1; while (i > 0) { i = (i - 1) >> 1; Tree[i] = f(Tree[(i << 1) + 1], Tree[(i << 1) + 2]); } } public void Query_Update(int ind, T val) { Assign(ind, val); Update(ind); } public T Query_Answer(int l, int r) //[l,r) { return Scanning(l, r, 0, 0, n); } private T Scanning(int l, int r, int ind, int ind_l, int ind_r) { if (ind_r <= l || r <= ind_l) { return ex; } if (l <= ind_l && ind_r <= r) { return Tree[ind]; } return f(Scanning(l, r, (ind << 1) + 1, ind_l, (ind_l + ind_r) >> 1), Scanning(l, r, (ind << 1) + 2, (ind_l + ind_r) >> 1, ind_r)); } public T Look(int ind) { return Tree[ind + n - 1]; } public void Debug_Display_All() { for (var i = 0; i < n; i++) Console.Write($"{Tree[i + n - 1]} "); Console.WriteLine(); } } struct ModInt { public long value; //private const int MOD = 1000000007; private const int MOD = 998244353; public ModInt(long value) { this.value = value; } public static implicit operator ModInt(long a) { var ret = a % MOD; return new ModInt(ret < 0 ? (ret + MOD) : ret); } public static ModInt operator +(ModInt a, ModInt b) => (a.value + b.value); public static ModInt operator -(ModInt a, ModInt b) => (a.value - b.value); public static ModInt operator *(ModInt a, ModInt b) => (a.value * b.value); public static ModInt operator /(ModInt a, ModInt b) => a * Modpow(b, MOD - 2); public static ModInt operator <<(ModInt a, int n) => (a.value << n); public static ModInt operator >>(ModInt a, int n) => (a.value >> n); public static ModInt operator ++(ModInt a) => a.value + 1; public static ModInt operator --(ModInt a) => a.value - 1; [MethodImpl(MethodImplOptions.AggressiveInlining)] public static ModInt Modpow(ModInt a, long n) { var k = a; ModInt ret = 1; while (n > 0) { if ((n & 1) != 0) ret *= k; k *= k; n >>= 1; } return ret; } private static readonly List Factorials = new List() { 1 }; [MethodImpl(MethodImplOptions.AggressiveInlining)] public static ModInt Fac(long n) { for (var i = Factorials.Count(); i <= n; i++) { Factorials.Add((Factorials[i - 1] * i) % MOD); } return Factorials[(int)n]; } [MethodImpl(MethodImplOptions.AggressiveInlining)] public static ModInt nCr(long n, long r) { return n < r ? 0 : Fac(n) / (Fac(r) * Fac(n - r)); } public static explicit operator int(ModInt a) => (int)a.value; } static class Cin { public static string[] ReadSplit => Console.ReadLine().Split(); public static int[] ReadSplitInt => ConvertAll(Console.ReadLine().Split(), int.Parse); public static long[] ReadSplitLong => ConvertAll(Console.ReadLine().Split(), long.Parse); public static double[] ReadSplit_Double => ConvertAll(Console.ReadLine().Split(), double.Parse); public static string Str => Console.ReadLine(); public static int Int => int.Parse(Console.ReadLine()); public static long Long => long.Parse(Console.ReadLine()); public static double Double => double.Parse(Console.ReadLine()); public static T Conv(string input) { if (typeof(T).Equals(typeof(ModInt))) { return (T)(dynamic)(long.Parse(input)); } return (T)Convert.ChangeType(input, typeof(T)); } public static void Input(out T a) => a = Conv(Console.ReadLine()); public static void Input(out T a, out U b) { var q = ReadSplit; a = Conv(q[0]); b = Conv(q[1]); } public static void Input(out T a, out U b, out V c) { var q = ReadSplit; a = Conv(q[0]); b = Conv(q[1]); c = Conv(q[2]); } public static void Input(out T a, out U b, out V c, out W d) { var q = ReadSplit; a = Conv(q[0]); b = Conv(q[1]); c = Conv(q[2]); d = Conv(q[3]); } public static void Input(out T a, out U b, out V c, out W d, out X e) { var q = ReadSplit; a = Conv(q[0]); b = Conv(q[1]); c = Conv(q[2]); d = Conv(q[3]); e = Conv(q[4]); } } static class Sc_out { public static void OutL(object s) => Console.WriteLine(s); public static void Out_Sep(IEnumerable s) => Console.WriteLine(string.Join(" ", s)); public static void Out_Sep(IEnumerable s, string sep) => Console.WriteLine(string.Join($"{sep}", s)); public static void Out_Sep(params object[] s) => Console.WriteLine(string.Join(" ", s)); public static void Out_One(object s) => Console.Write($"{s} "); public static void Out_One(object s, string sep) => Console.Write($"{s}{sep}"); public static void Endl() => Console.WriteLine(); } public static class Tool { static public void Initialize(ref T[] array, T initialvalue) { array = ConvertAll(array, x => initialvalue); } static public void Swap(ref T a, ref T b) { T keep = a; a = b; b = keep; } static public void Display(T[,] array2d, int n, int m) { for (var i = 0; i < n; i++) { for (var j = 0; j < m; j++) { Console.Write($"{array2d[i, j]} "); } Console.WriteLine(); } } static public long Gcd(long a, long b) { if (a == 0 || b == 0) return Max(a, b); return a % b == 0 ? b : Gcd(b, a % b); } static public long LPow(int a, int b) => (long)Pow(a, b); static public bool Bit(long x, int dig) => ((1L << dig) & x) != 0; static public int Sig(long a) => a == 0 ? 0 : (int)(a / Abs(a)); } }