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.Map.Entry;
import java.util.Scanner;
import java.util.TreeMap;


public class Main {
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();

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

    Entry<Integer, Integer> val = map.pollLastEntry();
    if (val.getValue()<2) {
      System.out.println(0);
    } else if (val.getValue()>3) {
      int key = val.getKey();
      System.out.println(key*key);
    } else {
      if (map.isEmpty()) {
        System.out.println(0);
      } else {
        Entry<Integer, Integer> val2 = map.pollLastEntry();
        if (val2.getValue()<2) {
          System.out.println(0);
        } else {
          int key = val.getKey();
          int key2 = val2.getKey();
          System.out.println(key*key2);
        }
      }
    }
    sc.close();
  }
}