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 C (GCC 9.2.1) (judge verdict: Runtime Error)

#include<stdio.h>
int main()
{
    int b[2]={0,0};
   int i,j,n,ara[10005],temp,c=0;
   scanf("%d",&n);
   for(i=0;i<n;i++)
   {
       scanf("%d",&ara[i]);
   }
   for(i=0;i<n;i++)
   {for(j=0;j<n;j++)
       {
           if(ara[i]>ara[j])
           {
               temp=ara[i];
               ara[i]=ara[j];
               ara[j]= temp;
           }
       }
   }
      for(i=0,j=0;i<n,j<2;i++)
      {
         if(ara[i]==ara[i+1])
            b[j++]=ara[i++];
      }
      printf("%d\n",b[0]*b[1]);
}