import java.io.*;
import java.util.*;
import java.text.*;
import java.math.*;
import java.util.regex.*;

public class Solution {

    static int[] A;
    static long largestValue() {
        // Return the largest value of any of A's nonempty subarrays.
        //int l=-1,r=-1;
        long sum =0;
        for(int l=0;l<A.length;l++)
        {
            for(int r = l;r<A.length;r++)
            {
                long k = computePairSum(l,r);
                if(k>sum)
                    sum=k;
                    
            }
        }
        return sum;
    }
    
    static long computePairSum(int l, int r)
    {
        long sum =0;
        for(int i=l;i<A.length;i++)
        {
            for(int j=i+1;j<=r;j++)
            {
                sum = sum + A[i]*A[j];
            }
        }
        return sum;
    }

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();
        A = new int[n];
        for(int A_i = 0; A_i < n; A_i++){
            A[A_i] = in.nextInt();
        }
        long result = largestValue();
        System.out.println(result);
        in.close();
    }
}