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 Java8 (OpenJDK 1.8.0) (judge verdict: Accepted)

import java.util.Arrays;
import java.util.Scanner;

/**
 * Created by Dmitry on 25.08.2017.
 */
public class Main {
    public static void main(String[] args) {
        //System.out.print("Hello");
        solve();
    }

    static void solve(){
        Scanner sc = new Scanner(System.in);

        int n = sc.nextInt();
        int[] arr = new int[n];
        for (int i=0;i<n;i++){
            arr[i]=sc.nextInt();
        }
        sc.close();
        Arrays.sort(arr);
        //long ans = 0;
        long max1=0;
        long max2 = 0;
        //int i = arr.length-1;
        for(int i = arr.length-1; i>=1;i--){
            if(arr[i-1] == arr[i]){
                if(max1==0){
                    max1 = arr[i];
                    i--;
                }
                else{
                    max2 = arr[i];
                    break;
                }
            }
        }
        long res = max1*max2;
        System.out.println(res);
    }
}