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)

fs = require('fs')
l = fs.readFileSync("/dev/stdin", "utf8")
  .split("\n")[1].split(' ').map(Number).sort();
function* gen(l){
  t = null;
  while(l.length > 0){
    a = l.pop();
    if(a===t){
      yield a;
      t = null;
    }
    else{
      t = a
    }
  }
}
g = gen(l)
x = g.next(); // console.log(x)
y = g.next(); // console.log(y)
if(y["done"]){
  console.log(0)
}
else{
  console.log(x.value*y.value)
}