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 N,i,j,tmp,M[2];
  long long int T;
  M[0]=0;
  M[1]=0;
  scanf("%d",&N);
  int a[N];
  for(i=0;i<N;i++){
    scanf("%d",&a[i]);
  }
  for (i=0; i<N; i++) {
    for (j=i+1; j<N; j++) {
      if (a[i] < a[j]) {
	tmp =a[i];
	a[i] = a[j];
	a[j] = tmp;
      }
    }
  }
  j=0;
  i=0;
  while(i<N-1 && j<2){
    if(a[i]==a[i+1]){
      M[j]=a[i];
      j++;
      i++;
    }
    i++;
  }
  T=M[0]*M[1];
  printf("%d",T);
  return 0;
}