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 5.4.1) (judge verdict: Runtime Error)

#include<stdio.h>
int main()
{
    int temp,a[1000],l,b;
        int n,i,j;
        l=0;
        b=0;
        scanf("%d",&n);
        for(i=0;i<n;i++)
    {
 
        scanf("%d",&a[i]);
    }
		for(i=0;i<n-1;i++)
		{
		  for(j=0;j<n-1-i;j++)
		  {
			if(a[j]<a[j+1])
			{
				temp=a[j];
				a[j]=a[j+1];
				a[j+1]=temp;
			}
		  }
		}
 
		for(i=0;i<n-1;i++)
		{
			if(a[i]==a[i+1])
			{
				l=a[i];
				//printf("\n%d",l);
				break;
			}
		}
		for(j=i+2;j<n-1;j++)
		{
			if(a[j]==a[j+1])
			{
				b=a[j];
//printf("\n%d",b);
				break;
			}
		}
		printf("%d",l*b);
 
    return 0;
}