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 Scala (2.11.7) (judge verdict: Accepted)

import java.util.Scanner

object Main {
  def solve(sc: => Scanner): Unit = {
    val Arr = Array.fill[Int](sc.nextInt)(sc.nextInt).groupBy(c => c).foldLeft[(Long, Long)]((0, 0))((A, B) => (
      if (B._2.length >= 4) ((math.max(A._1, B._1), math.max(A._2, B._1))) else if (B._2.length >= 2) (if (A._1 < A._2) ((math.max(A._1, B._1), A._2)) else ((A._1, math.max(A._2, B._1))))
      else (A)
      ))
    println(Arr._1 * Arr._2)
  }

  def main(args: Array[String]): Unit = {
    val sc: Scanner = new Scanner(System.in)
    solve(sc)
  }
}