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: Wrong Answer)


import java.util.*;

public class Main{

	public static void main(String[] args) {
		Scanner in=new Scanner(System.in); 
		int N=in.nextInt();
        int[] A=new int[N];
        long width=0,breadth=0;
        int i=0;
        Map<Integer,Integer> mp=new HashMap<>();
        while(N>i)
        {
            A[i]=in.nextInt();
            if(mp.get(A[i])==null)
            {
            	mp.put(A[i], 1);
            }
            else
            {
            	mp.put(A[i], mp.get(A[i])+1);
            }
            i++;
        }
         long prev=0;;
        for(Map.Entry<Integer, Integer> entry :mp.entrySet())
        {
        	if(entry.getValue()>=2&&entry.getValue()%4!=0)
			{
        		width=entry.getKey();
        		breadth=prev;
        		prev=width;
			}
        	if(entry.getValue()%4==0)
        	{	
        		width=breadth=entry.getKey();
        	}
        }
        System.out.println(width*breadth);
	}
}