import java.util.Scanner;

public class Solution {

    static long largestValue(int[] a) {
        long[][] sums = new long[a.length][a.length];
        long[][] aSums = new long[a.length][a.length];

        aSums[0][0] = a[0];
        for (int i = 1; i < a.length; i++) {
            aSums[0][i] = aSums[0][i - 1] + a[i];
        }
        for (int i = 1; i < a.length; i++) {
            for (int j = i; j < a.length; j++) {
                aSums[i][j] = aSums[i - 1][j] - a[i - 1];
            }
        }

        sums[0][1] = a[0] * a[1];

        for (int i = 2; i < a.length; i++) {
            sums[0][i] = sums[0][i - 1] + a[i] * aSums[0][i - 1];
        }

        for (int i = 1; i < a.length; i++) {
            for (int j = i + 1; j < a.length; j++) {
                sums[i][j] = sums[i - 1][j] - a[i - 1] * aSums[i][j];
            }
        }

        long result = Long.MIN_VALUE;
        for (int i = 0; i < a.length; i++) {
            for (int j = 0; j < a.length; j++) {
                if (sums[i][j] > result) {
                    result = sums[i][j];
                }
            }
        }
        return result;
    }

    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();
    }
}