using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;

namespace AtCoder.A
{
    public class Program
    {
        public static void Main() { var r = GetResult(); Debug.WriteLine(r); Console.Write(r); }

        private static object GetResult()
        {
            var N = ReadLong();
            var A = ReadLongs();

            var min = long.MaxValue;
            for (var i = 0; i < N - 2; i++)
            {
                for (var j = i + 1; j < N - 1; j++)
                {
                    for (var k = j + 1; k < N; k++)
                    {
                        var a = A[i];
                        var b = A[j];
                        var c = A[k];

                        if (a == b || b == c || c == a) continue;
                        if (b < a && b < c || b > a && b > c)
                        {
                            min = Math.Min(min, a + b + c);
                        }
                    }
                }
            }

            return min == long.MaxValue ? -1 : min;
        }

        #region Console

        public static string ReadText() { return Console.ReadLine(); }
        public static List<string> ReadTexts() { return Console.ReadLine().Split(' ').ToList(); }
        public static long ReadLong() { return long.Parse(Console.ReadLine()); }
        public static List<long> ReadLongs() { return Console.ReadLine().Split(' ').Select(x => long.Parse(x)).ToList(); }

        #endregion
    }
}