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 Java (OpenJDK 11.0.6) (judge verdict: Accepted)

import java.util.*;
public class Main {
	
	public static void main (String[] args)
	{
		Scanner sc = new Scanner (System.in);
		int nums = sc.nextInt();
		long[] arr = new long[2];
		long[] sticks = new long[nums];
		for (int i= 0; i < nums; i++)
			sticks[i]=sc.nextInt();
		Arrays.sort(sticks);
		int count = 0;
		//for (int i = nums - 1; i >= 1; i--)
		while(nums -- > 1)
		{
			if (sticks[nums]==sticks[nums-1])
			{
				arr[count]= sticks[nums];
				nums--;
				count++;
			}
			if (count==2)
				break;
		}
			System.out.println(arr[0]*arr[1]);
		
	}
	
	
	
}