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: Runtime Error)




object Main extends App {
	import scala.io.StdIn._
	import scala.math._

	def sort(x: List[Long]): List[Long] = {
		x match {
			case Nil => List[Long]()
			case r::Nil => List(r)
			case r::rest =>{
				val temp = rest.toArray
				var right = List(r)
				var left = List[Long]()

				for(i<-0 until rest.size){
					if(temp(i) > r) right = temp(i)::right
					else left = temp(i)::left
				}

				sort(left):::sort(right)
			}
		}
	}
	
	val N = readInt
	val A = readLine.split(" ").map(_.toLong).toList

	val AA = sort(A).reverse

	var result = new Array[Long](5)
	var j = 0

	for(i <- AA){
		result(j) = i
		j match {
			case 0 => j = j + 1
			case 1 if(result(0) != result(1)) => result(0) = i
			case 1 if(result(0) == result(1)) => j = j + 1
			case 2 => j = j + 1
			case 3 if(result(0) != result(1)) => result(2) = i
			case 3 if(result(0) == result(1)) => j = j + 1
			case _ => 
		}
	}

	println(min(result(0),result(1)) * min(result(2),result(3)))
}