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 JavaScript (node.js v5.12) (judge verdict: Wrong Answer)

function Main(input) {
  input = input.split("\n");
  var n = parseInt(input[0].split(" ")[0]);
  tmp = input[1].split(" ");
  a = new Array(n).fill(0);
  for(i=0;i<n;i++){
    a[i]=parseInt(tmp[i]);
  }
  var ans = 0;
  a.sort(function(a,b){
    if( a > b ) return -1;
    if( a < b ) return 1;
    return 0;
  });
  var x =0;
  var y =0;
  for(i=0;i<n-1;i++){
    if(a[i]==a[i+1]){
      if(a[i]>x){
        x=a[i];
      }else if(a[i]>y&&a[i]!=x){
        y=a[i];
      }
    }
  }
  ans = x * y;
  if(x!=0&&y==0){
    var b="";
    for(i=0;i<n;i++){
      b+=a[i];
    }
    var reg = new RegExp(x,"g");
    if((b.match(reg)).length>=4){
      ans=Math.pow(x,2);
    }
  }
  console.log('%s', ans);
}
Main(require("fs").readFileSync("/dev/stdin", "utf8"));