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;
  scanf("%d",&N);
  long A[N];
  int one=0,two=0;
  for(int i=0;i<N;i++){
    scanf("%ld",&A[i]);
      for(int j=0;j<i;j++){

        if(A[i]==A[j]){
          if(A[j]>one && one!=A[j]){
            two=one;
            one=A[j];
          }
          else if(A[j]>two && two!=A[j] && A[j]!=one){
            two=A[j];
          }
        }

      }
  }
  printf("%d\n",one*two);
}