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 temp = 0;
        TreeSet<Integer> sum = new TreeSet<Integer>();
        for(int i=0; i<a.length; i++) {
            for(int j=i+1; j<a.length; j++) {
                temp = a[i]*a[j];
                sum.add(temp);
            }
        }
        return sum.last();
    }

    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();
    }
}