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: Accepted)

import java.util.*;
import java.math.*;

public class Main {

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

    for (int i = 0; i < n; i++) {
      a[i] = sc.nextLong();
    }

    Arrays.sort(a);

    long x = 0;
    long y = 0;
    int k = 0;

    for (int i = n-1; i > 0; i--) {
      if (a[i] == a[i-1]) {
        x = a[i];
        k = i;
        break;
      }
    }

    for (int i = k-2; i > 0; i--) {
      if (a[i] == a[i-1]) {
        y = a[i];
        break;
      }
    }

    System.out.println(x*y);
    
  }

}