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

public class JavaApplication1 {

    static long largestValue(int[] a) {
        // Return the largest value of any of A's nonempty subarrays.
    ArrayList<Long> arr=new ArrayList<>();
    long sum=0;
  
    
    for(int i=0;i<a.length;i++){
        {
            sum=0;
            int k=0;
            while(k!=a.length){
                sum=0;
            
            for(int j=0;j<a.length;j++)
            {
                if(j==k && j==i)
                    continue;
                else
                    sum+=a[i]*a[j];
                
            }
            k++;
                arr.add(sum);
                }
        }
        
                }
    
    
    
    Collections.sort(arr,Collections.reverseOrder());
long ans=arr.get(0);
    return  ans; 
    }

    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();
    }
}