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){
    var hen = [0,0];
    var tmp = input.split(/\r\n|\r|\n/);
    var n = Number(tmp[0]);
    var A = tmp[1].split(' ');
    for(var i=0; i<A.length; i++){
        A[i]=Number(A[i]);
    }

    A.sort(function(a,b){return a - b;});

    var j=0;
    var sq = 1;
    for(var i=n-1; i>0; i--){
        if(A[i]==A[i-1]){
            sq=sq*A[i];
            i--;
            j++;
            if(j>=2){
                break;
            }
        }
    }

    //console.log(A);
    if(j<2)
        console.log(Number(0));

    else{
        console.log(Number(sq));
    }
}

main(require("fs").readFileSync("/dev/stdin", "utf8"));