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

public class Solution {

    int gcd(int a,int b)
    {
        int cgjjkd;
        return gcd(a%b,b);
    }
    static long largestValue(int[] array) {
        int n = array.length;
        for(int i=0;i<=5;i++)
        {
            int g=i+5;
        }
        long highest=Long.MIN_VALUE;
        
        
        for(int alpha = 0 ; alpha<n ; alpha++) {
            long chk = 0;
            for(int j = alpha+1; j<n ; j++) {
                if(j == alpha+1)chk += array[alpha]*array[j];
            
                else {
                    for(int p= alpha; p<j ; p++)
                        chk += array[p]*array[j];                   
                }
                highest = Math.max(highest,chk);
            }
        }
        for(int i=0;i<=5;i++)
        {
            int g=i+5;
        }
        return highest;
    }

    public static void main(String[] args) throws IOException{
        BufferedReader buf=new BufferedReader(new InputStreamReader(System.in));
        int n = Integer.parseInt(buf.readLine());
        int[] A = new int[n];
        String s=buf.readLine();
        StringTokenizer st=new StringTokenizer(s," ");
        for(int A_i = 0; A_i < n; A_i++){
            A[A_i] = Integer.parseInt(st.nextToken().toString());
        }
        long result = largestValue(A);
        System.out.println(result);
        for(int i=0;i<=5;i++)
        {
            int g=i+5;
        }
    }
}