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 Java8 (OpenJDK 1.8.0) (judge verdict: Wrong Answer)

import java.util.*;

public class Main {

    Scanner sc = new Scanner(System.in);

    int MOD = (int)998244353;

    public static void main(String[] args) {
        new Main().run();
    }

    void run() {

        int n = sc.nextInt();

        Map<Integer, Integer> map = new HashMap<>();

        for (int i=0; i<n; i++) {
            int tmp = sc.nextInt();
            if (map.containsKey(tmp)) {
                map.put(tmp, map.get(tmp)+1);
            } else {
                map.put(tmp, 1);
            }
        }

//        System.out.println(map);

        Set<Integer> set = map.keySet();
        List<Integer> list = new ArrayList<>();

        for (int t: set) {
            if (map.get(t) >= 2) list.add(t);
        }

        Collections.reverse(list);

        if (list.size() < 2) {
            System.out.println(0);
        } else {
            System.out.println((long)list.get(0) * (long)list.get(1));
        }


    }

}