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++14 (GCC 5.4.1) (judge verdict: Runtime Error)

#include<stdio.h>
int n,i,j,p,m,x,y,a[100000];
int main()
{
	scanf("%d",&n);
	for(i=0;i<n;i++){
		scanf("%d",&p);
		a[p]++;
		if(a[p]>1&&m<p){
			m=p;
		}
	}
	for(i=m;i;i--){
		if(a[i]>3){
			x=i;
			y=i;
			break;
		}
		if(a[i]>1){
			x=i;
			m=i-1;
			break;
		}
	}
	for(i=m;i;i--){
		if(a[i]>1&&x>i){
			y=i;
			break;
		}
	}
	printf("%d\n",x*y);
	return 0;
}