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 C# (Mono 4.6.2.0) (judge verdict: Wrong Answer)

using System;
using System.Linq;

namespace AtCoder
{
    class Program
    {
        static void Main()
        {
            int n = int.Parse(Console.ReadLine());
            var a = Array.ConvertAll(Console.ReadLine().Split(), int.Parse);
            a = a.OrderByDescending(i => i).ToArray();
            int L1 = 0, L2 = 0, temp = a[0];
            for (int i = 0; i < a.Count() - 1; i++)
            {
                if (L2 != 0) break;
                else if (temp == a[i + 1])
                {
                    L2 = L1;
                    L1 = temp;
                    temp = 0;
                }
                else temp = a[i + 1];
            }
            Console.WriteLine(L1 * L2);
        }
    }
}