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

public class Solution {

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

    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();
    }
}