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

public class Solution {

    static long h = Long.MIN_VALUE;
    
    static long largestValue(int[] a) {
        int n = a.length;
        
        for(int i = 0 ; i<n ; i++) {
            long c = 0;
            for(int j = i+1; j<n ; j++) {
                if(j == i+1) {
                    c += a[i]*a[j];
                }
                else {
                    for(int k = i; k<j ; k++) {
                        c += a[k]*a[j];
                    }
                }
                h = Math.max(h,c);
            }
        }
        
        return h;
    }

    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();
    }
}