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 Kotlin (1.0.0) (judge verdict: Wrong Answer)

import java.util.*

fun main(args: Array<String>) {
    val sc = Scanner(System.`in`)
    val n = sc.nextInt()
    val a = (0 until n).map { sc.next().toLong() }
    answer071cAlt(n, a)
}

fun answer071cAlt(n: Int, a: List<Long>) {
    val reversedA: MutableList<Long> = a.sortedDescending() as MutableList<Long>

    val set: MutableList<Long> = mutableListOf<Long>()
    var count = 0
    var firstFlg = false
    for (index: Int in reversedA.indices) {
        if (index == 0) {
            continue
        }
        if (reversedA[index] == reversedA[index - 1] && !firstFlg) {
                count += 1
                set.add(reversedA[index])
                firstFlg = true


            if (count == 2) {
                println(set)
                break
            }
        }else {
            firstFlg = false
        }
    }
    if (set.isEmpty()) {
        println(0)
    } else  {
        println(set[0] * set[1])
    }
}