using System; using System.Collections.Generic; using System.Linq; using System.IO; using System.Threading; using System.Runtime.CompilerServices; using System.Text; using System.Diagnostics; using System.Numerics; using static System.Console; using static System.Convert; using static System.Math; using static Template; using Pi = Pair; class Solver { public Scanner sc; public void Solve() { var N = sc.Int; var A = sc.ArrInt; var idx = Enumerable.Range(0, N).Shuffle().OrderBy(v => A[v]).ToArray(); var seg = new SegmentTree(N, int.MaxValue / 2, Min); var res = int.MaxValue / 2; foreach (var i in idx) { var L = seg.Query(0, i); var R = seg.Query(i, N); seg.Update(i, A[i]); if (L == int.MaxValue / 2 || R == int.MaxValue / 2) continue; chmin(ref res, L + R + A[i]); } Array.Reverse(idx); seg= new SegmentTree(N, int.MaxValue / 2, Min); foreach (var i in idx) { var L = seg.Query(0, i); var R = seg.Query(i, N); seg.Update(i, A[i]); if (L == int.MaxValue / 2 || R == int.MaxValue / 2) continue; chmin(ref res, L + R + A[i]); } if (res == int.MaxValue / 2) Fail(-1); Console.WriteLine(res); } } public class SegmentTree { protected readonly T[] dat; protected readonly int sz; protected readonly Func merge; protected readonly Func update; protected readonly T id; private bool finished = true; [MethodImpl(MethodImplOptions.AggressiveInlining)] protected int Left(int i) => i << 1; [MethodImpl(MethodImplOptions.AggressiveInlining)] protected int Right(int i) => (i << 1) | 1; public T this[int i] { get { return dat[i + sz]; } set { finished = false; dat[i + sz] = value; } } public SegmentTree(int N, T id, Func merge, Func update = null) { this.sz = 1; while (sz < N) sz <<= 1; this.id = id; this.merge = merge; this.update = update ?? ((T val1, T val2) => val2); dat = Create(sz << 1, () => id); } public void Update(int i, T value) { i += sz; dat[i] = update(dat[i], value); while (i > 1) { i >>= 1; dat[i] = merge(dat[Left(i)], dat[Right(i)]); } } public void Build() { for (int i = sz - 1; i > 0; i--) dat[i] = merge(dat[Left(i)], dat[Right(i)]); finished = true; } public virtual T Query(int left, int right) { if (!finished) throw new Exception("You need to Execute \"Build()\""); T l = id, r = id; for (left += sz, right += sz; left < right; left >>= 1, right >>= 1) { if ((left & 1) == 1) l = merge(l, dat[left++]); if ((right & 1) == 1) r = merge(dat[--right], r); } return merge(l, r); } public int Find(int st, Func check) { var x = id; return Find(st, check, ref x, 1, 0, sz); } private int Find(int st, Func check, ref T x, int k, int l, int r) { if (l + 1 == r) { x = merge(x, dat[k]); return check(x) ? k - sz : -1; } var m = (l + r) >> 1; if (m <= st) return Find(st, check, ref x, Right(k), m, r); if (st <= l && !check(merge(x, dat[k]))) { x = merge(x, dat[k]); return -1; } var xl = Find(st, check, ref x, Left(k), l, m); if (xl >= 0) return xl; return Find(st, check, ref x, Right(k), m, r); } } #region Template public static class Template { static void Main(string[] args) { Console.SetOut(new StreamWriter(Console.OpenStandardOutput()) { AutoFlush = false }); var sol = new Solver() { sc = new Scanner() }; //var th = new Thread(sol.Solve, 1 << 26);th.Start();th.Join(); sol.Solve(); Console.Out.Flush(); } [MethodImpl(MethodImplOptions.AggressiveInlining)] public static bool chmin(ref T a, T b) where T : IComparable { if (a.CompareTo(b) > 0) { a = b; return true; } return false; } [MethodImpl(MethodImplOptions.AggressiveInlining)] public static bool chmax(ref T a, T b) where T : IComparable { if (a.CompareTo(b) < 0) { a = b; return true; } return false; } [MethodImpl(MethodImplOptions.AggressiveInlining)] public static void swap(ref T a, ref T b) { var t = b; b = a; a = t; } [MethodImpl(MethodImplOptions.AggressiveInlining)] public static void swap(this IList A, int i, int j) { var t = A[i]; A[i] = A[j]; A[j] = t; } public static T[] Create(int n, Func f) { var rt = new T[n]; for (var i = 0; i < rt.Length; ++i) rt[i] = f(); return rt; } public static T[] Create(int n, Func f) { var rt = new T[n]; for (var i = 0; i < rt.Length; ++i) rt[i] = f(i); return rt; } public static IEnumerable Shuffle(this IEnumerable A) => A.OrderBy(v => Guid.NewGuid()); public static int CompareTo(this T[] A, T[] B, Comparison cmp = null) { cmp = cmp ?? Comparer.Default.Compare; for (var i = 0; i < Min(A.Length, B.Length); i++) { int c = cmp(A[i], B[i]); if (c > 0) return 1; else if (c < 0) return -1; } if (A.Length == B.Length) return 0; if (A.Length > B.Length) return 1; else return -1; } public static int ArgMax(this IList A, Comparison cmp = null) { cmp = cmp ?? Comparer.Default.Compare; T max = A[0]; int rt = 0; for (int i = 1; i < A.Count; i++) if (cmp(max, A[i]) < 0) { max = A[i]; rt = i; } return rt; } public static T PopBack(this List A) { var v = A[A.Count - 1]; A.RemoveAt(A.Count - 1); return v; } public static void Fail(T s) { Console.WriteLine(s); Console.Out.Close(); Environment.Exit(0); } } public class Scanner { public string Str => Console.ReadLine().Trim(); public int Int => int.Parse(Str); public long Long => long.Parse(Str); public double Double => double.Parse(Str); public int[] ArrInt => Str.Split(' ').Select(int.Parse).ToArray(); public long[] ArrLong => Str.Split(' ').Select(long.Parse).ToArray(); public char[][] Grid(int n) => Create(n, () => Str.ToCharArray()); public int[] ArrInt1D(int n) => Create(n, () => Int); public long[] ArrLong1D(int n) => Create(n, () => Long); public int[][] ArrInt2D(int n) => Create(n, () => ArrInt); public long[][] ArrLong2D(int n) => Create(n, () => ArrLong); private Queue q = new Queue(); [MethodImpl(MethodImplOptions.AggressiveInlining)] public T Next() { if (q.Count == 0) foreach (var item in Str.Split(' ')) q.Enqueue(item); return (T)Convert.ChangeType(q.Dequeue(), typeof(T)); } public void Make(out T1 v1) => v1 = Next(); public void Make(out T1 v1, out T2 v2) { v1 = Next(); v2 = Next(); } public void Make(out T1 v1, out T2 v2, out T3 v3) { Make(out v1, out v2); v3 = Next(); } public void Make(out T1 v1, out T2 v2, out T3 v3, out T4 v4) { Make(out v1, out v2, out v3); v4 = Next(); } public void Make(out T1 v1, out T2 v2, out T3 v3, out T4 v4, out T5 v5) { Make(out v1, out v2, out v3, out v4); v5 = Next(); } public void Make(out T1 v1, out T2 v2, out T3 v3, out T4 v4, out T5 v5, out T6 v6) { Make(out v1, out v2, out v3, out v4, out v5); v6 = Next(); } public void Make(out T1 v1, out T2 v2, out T3 v3, out T4 v4, out T5 v5, out T6 v6, out T7 v7) { Make(out v1, out v2, out v3, out v4, out v5, out v6); v7 = Next(); } //public (T1, T2) Make() { Make(out T1 v1, out T2 v2); return (v1, v2); } //public (T1, T2, T3) Make() { Make(out T1 v1, out T2 v2, out T3 v3); return (v1, v2, v3); } //public (T1, T2, T3, T4) Make() { Make(out T1 v1, out T2 v2, out T3 v3, out T4 v4); return (v1, v2, v3, v4); } } public class Pair : IComparable> { public T1 v1; public T2 v2; public Pair() { } public Pair(T1 v1, T2 v2) { this.v1 = v1; this.v2 = v2; } [MethodImpl(MethodImplOptions.AggressiveInlining)] public int CompareTo(Pair p) { var c = Comparer.Default.Compare(v1, p.v1); if (c == 0) c = Comparer.Default.Compare(v2, p.v2); return c; } public override string ToString() => $"{v1.ToString()} {v2.ToString()}"; public void Deconstruct(out T1 a, out T2 b) { a = v1; b = v2; } public static implicit operator Pair((T1 f, T2 s) p) => new Pair(p.f, p.s); } public class Pair : Pair, IComparable> { public T3 v3; public Pair() : base() { } public Pair(T1 v1, T2 v2, T3 v3) : base(v1, v2) { this.v3 = v3; } [MethodImpl(MethodImplOptions.AggressiveInlining)] public int CompareTo(Pair p) { var c = base.CompareTo(p); if (c == 0) c = Comparer.Default.Compare(v3, p.v3); return c; } public override string ToString() => $"{base.ToString()} {v3.ToString()}"; public void Deconstruct(out T1 a, out T2 b, out T3 c) { Deconstruct(out a, out b); c = v3; } public static implicit operator Pair((T1 f, T2 s, T3 t) p) => new Pair(p.f, p.s, p.t); } #endregion