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)

fun main(args: Array<String>) {
    val n = readLine()!!.toInt()
    val aList = readLine()!!.split(' ').map(String::toLong)
    var map = mutableMapOf<Long, Long>()
    aList.forEach {
        if (map.containsKey(it)) {
            map[it] = map[it]!! + 1L
        } else {
            map[it] = 1L
        }
    }
    val countMap = map.filterValues { it >= 2L }
    if (countMap.size < 2) {
        println(0)
        return
    }
    val (first, second) = countMap.keys.toList().sortedDescending().subList(0, 2)
    println(first * second)
}