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.*;
public class Main{
    public static void main(String[]args){
        Scanner sc=new Scanner(System.in);
        int N=sc.nextInt();
        int[]A=new int[N];
        for(int i=0;i<N;i++){
            A[i]=sc.nextInt();
        }
        Arrays.sort(A);
        Set<Integer>youso=new HashSet<Integer>();
        for(int i=0;i<N-1;i++){
            if(A[i]==A[i+1]){
                youso.add(A[i]);
            }
        }
        int max=0;
        for(int a:youso){
            if(max<a){
                max=a;
            }
        }
        int maxx=0;
        for(int a:youso){
            if((maxx<a)&&(a<max)){
                maxx=a;
            }
        }
        System.out.println(max);
        System.out.println(maxx);
        System.out.println(max*maxx);
        }
       
        
    }