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.Scanner;
import java.util.Arrays;

public class Main {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int N = sc.nextInt();
        long A[] = new long[N];
        long array[] = new long[N];
        long yoko = 0, tate = 0;
        int l = 0;
        long tmp = 0;
        for (int i = 0; N > i; i++) {
            A[i] = sc.nextLong();
        }
        Arrays.sort(A);
        for (int j = N-1; 0 <= j; j--) {
            if (tmp != A[j]) {
                tmp = A[j];
            } else {
                yoko = A[j];
                l = j;
                break;
            }
        }
        tmp = 0;
        for (int k = l - 1; 0 <= k; k--) {
            if (tmp != A[k]) {
                tmp = A[k];
            } else {
                tate = A[k];
                break;
            }
        }
        System.out.println(yoko * tate);
    }
}