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 seq = Range(0, n).map(_ => sc.nextInt())
    .groupBy(i => i)
    .toStream
    .sortWith((t1, t2) => t1._1 > t2._1)
    .filter(t => t._2.size > 1)
    .toSeq

  if (seq.size == 1) {
    println(if (seq(0)._2.size > 3) seq(0)._1 * seq(0)._1 else 0)
  }else if (seq.size > 1) {
    println(if (seq(0)._2.size > 3) seq(0)._1 * seq(0)._1 else seq(0)._1 * seq(1)._1)
  } else {
    println(0)
  }
}