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 max1 = 0;
    var max2 = 0;
    var once = [];

    var tmp = input.split('\n');
    var A = tmp[1].split(' ');

    var index;
    for(var i=0; i<A.length; i++){
        index = once.indexOf(A[i]);
        if(index===-1){
            once.push(A[i]);
        }
        else{
            once.splice(index,1);
            if(max2<A[i]){
                if(max1<A[i]){
                    max2 = max1;
                    max1 = A[i];
                }else{
                    max2 = A[i];
                }
            }
        }
    }
    console.log(max2*max1);

}

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