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) {
      	final Scanner sc = new Scanner(System.in);
      	final int N = sc.nextInt();
      	final int[] A = new int[N];
      	for(int i = 0; i < N; i++)
        	A[i] = sc.nextInt();
      	Arrays.sort(A);
      	long longer = 0;
      	for(int i = N - 1, p = -1; i >= 0; i--)
        	if(p == A[i]) {
            	if(longer > 0) {
                	System.out.println(longer * p);
                  	return;
                } else {
                	longer = p;
                  	p = -1;
                }
            } else
              	p = A[i];
      	System.out.println(0);
    }
}