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.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.Scanner;
import java.util.TreeMap;
public class Main{
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    int n=sc.nextInt();
    List<Integer> list=new ArrayList<>();
    Map<Integer,Integer> map=new TreeMap<>();
    for(int i=0;i<n;i++) {
    	int buff=sc.nextInt();
    	if(map.containsKey(buff)) {
    		map.put(buff, map.get(buff)+1);
    	}else {
    		map.put(buff, 1);
    	}
    }
    for (Integer key : map.keySet()){
    	if(map.get(key)>=2) {
    		list.add(key);
    	}
    }
    if(list.size()>=2)System.out.println(list.get(list.size()-1)*list.get(list.size()-2));
    else System.out.println(0);
  }
}