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

public class Solution {
    
    static long POI(int[] A) {
        long sum = 0;
        for (int i = 0; i < A.length; i++) {
            for (int j = i+1; j < A.length; j++) {
                sum += A[i] * A[j];
            }
        }
        return sum;
    }
    
    static long largestValue(int[] A) {
        long max = POI(A);
        int length = A.length-1;
        int index = 0;
        while (length > 0) {
            index = 0;
            while (index + length < A.length) {
                long val = POI(Arrays.copyOfRange(A, index, index+length));
                if (val > max) max = val;
                index++;
            }
            length--;
        }
        return max;
    }

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