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 Java7 (OpenJDK 1.7.0) (judge verdict: Wrong Answer)

import java.util.*;

class Main{
  public static void main(String args[]){
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();
    int[] len = new int[n];
    int tmp,w=0,h=0;
    int flag = 0;

    for(int i=0;i<n;i++){
      len[i] = sc.nextInt();
    }
    Arrays.sort(len);
    tmp = len[n-1];
    for(int i=1;i<n;i++){
      if(tmp == len[n-1-i] && flag == 0){
        w = tmp;
        flag = 1;
        tmp = 0;
      }else if(tmp == len[n-1-i] && flag == 1){
        h = tmp;
        break;
      }else{
        tmp = len[n-1-i];
      }
    }
    System.out.println(w*h);
  }
}