Problem:
Score : 300 points

Problem Statement

We have N sticks with negligible thickness.
The length of the i-th stick is A_i.

Snuke wants to select four different sticks from these sticks and form a rectangle (including a square), using the sticks as its sides.
Find the maximum possible area of the rectangle.

Constraints

4 \leq N \leq 10^5

1 \leq A_i \leq 10^9

A_i is an integer.

Input

Input is given from Standard Input in the following format:

N
A_1 A_2 ... A_N

Output

Print the maximum possible area of the rectangle.
If no rectangle can be formed, print 0.

Sample Input 1

6
3 1 2 4 2 1

Sample Output 1

2

1 \times 2 rectangle can be formed.

Sample Input 2

4
1 2 3 4

Sample Output 2

0

No rectangle can be formed.

Sample Input 3

10
3 3 3 3 4 4 4 5 5 5

Sample Output 3

20

Solution in Java (OpenJDK 11.0.6) (judge verdict: Wrong Answer)

import java.util.*;
public class Main{
        public static void main(String[] args){
                Scanner sc = new Scanner(System.in);
                int n = sc.nextInt();
                int[] 鶏 = new int[n];
                for(int i = 0 ; i < n ; i++){
                        鶏[i] = sc.nextInt();
                }
                int[] 烏 = new int[2];
                Arrays.fill(烏 , 0);
                int 鷹 = 0;
                sc.close();
                Arrays.sort(鶏);
                for(int i = n - 1 ; i > 0 && 鷹 < 2 ; i--){
                        if(鶏[i] == 鶏[i - 1]){
                                i--;
                                烏[鷹] = 鶏[i + 1];
                                鷹++;
                        }
                }
                System.out.println(烏[0] * 烏[1]);
        }
}