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 max = 0;
        for(int i = 0; i < A.length - 1; ++i){
            for(int j = i + 1; j < A.length; ++j){
                long value = 0;
                for(int k = i; k < j; ++k){
                    for(int l = k + 1; l <= j; ++l){
                        //System.out.print(A[k] + "*" + A[k + 1] + " ");
                        value += A[k] * A[l];
                    }
                }
                //System.out.println(value);
                if(value > max) max = value;
            }
        }
        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();
    }
}