using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
class Solution {

    static long largestValue(int[] A) {
        
        long maxValue = long.MinValue;
        
        for(int i = 0; i < A.Length; ++i)
        {
            for(int j = i; j < A.Length; ++j)
            {
                if(i+j < A.Length)
                {
                    var subArray = A.Skip(i).Take(j+1).ToArray();

                    //Console.WriteLine($"{i},{j}="+ string.Join(",", subArray));

                    long max = GetMax(subArray);
                    if(max > maxValue)
                    {
                        maxValue = max;
                    }
                }
            }
        }
        
        return maxValue;
    }

    static long GetMax(int[] A)
    {
        long sum = 0;
        
        for(int i = 0; i < A.Length-1; ++i)
        {
            for(int j = 1; j < A.Length; ++j)
            {
                if(j!=i && j>i)
                {
                    //Console.WriteLine($"{A[i]},{A[j]}");
                    sum += A[i]*A[j];
                }
            }
        }
        
        //Console.WriteLine($"-----");
        return sum;
    }
    
    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);
    }
}