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

public class Solution {

    static long largestValue(int[] A) {
        long largest = Long.MIN_VALUE;
        for(int i = 0; i < A.length; i++) {
            for(int j = i; j < A.length; j++) {
                int start = i;
                int end = j;
                
                long sum = 0;
                for(int k = start; k <= end; k++) {
                    for(int l = k + 1; l <= end; l++) {
                        sum += A[k] * A[l];
                    }
                }
                
                largest = Math.max(largest, sum);
            }
        }
        return largest;
    }

    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();
    }
}