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: Runtime Error)

import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int N = sc.nextInt();
        int A[] = new int[N];
        int ans[] = new int[100000];
        int tate = 0;
        int yoko = 0;
        for (int i = 0; N > i; i++) {
            A[i] = sc.nextInt();
        }
        for (int j = 0; N > j; j++) {
            ans[A[j]]++;
        }
        lavel:for (int a = 10000; 0 <= a; a--) {
            if (ans[a] >= 2) {
                tate = a;
                ans[a] = ans[a] - 2;
                for(int b=a;0<=b;b--){
                    if(ans[b]>=2){
                        yoko=b;
                        break lavel;
                    }
                }
            }
        }
        System.out.println(tate * yoko);
    }
}