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.*;

public class Main {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n=sc.nextInt();
        long[] nums=new long[n];
        for(int i=0;i<n;i++){
            nums[i]=sc.nextInt();
        }
        Arrays.sort(nums);
        int count=0;
        long ans=1;
        for(int i=n-1;i>0;i--){
            if(count==0&&nums[i]==nums[i-1]){
                ans=nums[i];
                count++;
                i--;
            }else if(count==1&&nums[i]==nums[i-1]){
                System.out.println(ans*nums[i]);
                return;
            }
        }
        System.out.println(0);
    }
}