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: Wrong Answer)

import java.util.Scanner

object Main extends App {
  val sc = new Scanner(System.in)
  val N = sc.nextInt
  val A = (0 until N).map(_ => sc.nextInt)
  val dup = A.groupBy(identity).toSeq.flatMap(t => (Seq.fill(t._2.size / 2)(t._1))).sorted(Ordering[Int].reverse)
  println((dup ++ Seq(0, 0)).take(2).reduce(_ * _))
}