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

class Solution {

    static long largestValue(int[] A) {
        long res = 0;
            var x = GetAllCombos(A.ToList());
            x.RemoveAll(z => z.Count != 2);
            var y = new List<long>();
            foreach (var item in x)
            {
                y.Add(item[0] * item[1]);
            }
            res = y.Sum();

            return res;
    }

    static void Main(String[] args) {
        int n = Convert.ToInt32(Console.ReadLine());
        string[] A_temp = Console.ReadLine().Split(' ');
        int[] A = Array.ConvertAll(A_temp,Int32.Parse);
        long result = largestValue(A);
        Console.WriteLine(result);
    }
    
    public static List<List<T>> GetAllCombos<T>(List<T> list)
        {
            List<List<T>> result = new List<List<T>>();
            // head
            result.Add(new List<T>());
            result.Last().Add(list[0]);
            if (list.Count == 1)
                return result;
            // tail
            List<List<T>> tailCombos = GetAllCombos(list.Skip(1).ToList());
            tailCombos.ForEach(combo =>
            {
                result.Add(new List<T>(combo));
                combo.Add(list[0]);
                result.Add(new List<T>(combo));
            });
            return result;
        }
}