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: Wrong Answer)

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