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.
        int i,j,k,l=A.length,m,max=0,temp;;
        for(i=0;i<l-2;i++) {
            for(j=i+2;j<=l;j+=2) {
                //System.out.println(i+"->"+j);
                temp=0;
                for(k=i;k<j-1;k++) {
                    for(m=k+1;m<j;m++) {
                        //System.out.println(k+"*"+m+", ");
                        temp+=A[k]*A[m];
                    }
                    //System.out.println();
                }
                if(temp>max) max=temp;
            }
        }
        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();
    }
}