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: Wrong Answer)

#include<stdio.h>
int main()
{
    int s[100000] ,b[100];
    int n,a,i,c,k=0,j,l=0,m,temp;
    scanf("%d ",&n);
    for(i=0;i<n;i++){
        scanf("%d",&a);
        s[i]=a;
    }
    for(i=0;i<n;i++){
            c=0;
        for(j=0;j<n;j++){
            if(s[i]==s[j]){
                c++;
            }
        }
        if(c>=2){
    b[l]=s[i];
    l++;
     k++;
    }
    }
    if(k==0){
        printf("0");

    }
     for(l=0; l<k-1; l++)
    {
        for(m=l+1; m<k; m++)
        {
            if(b[l]<b[m])
            {
                temp=b[l];
                b[l]=b[m];
               b[m]=temp;
            }
        }
    }
    for(l=0;l<k;l++){
            if(b[0]>b[l]){
        printf("%d ",b[0]*b[l]);
        break;
            }
   }
 return 0;
}