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

public class Solution {

    static long largestValue(int[] A) {
       int i,j,k,large=0;
        for(int t=1;t<A.length;t++){
        for(i=0;i<t;i++)
        {
            int sum=0;
            for(j=i;j<t;j++)
            {
                for(k=j+1;k<t;k++)
                {
                    sum+=(A[j]*A[k]);
                }
            }
           // System.out.println(sum);
            if(sum>large)large=sum;
        } 
        }
        return large;
    }

    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();
    }
}