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)

'use strict'

function Main(input) {
  const inputs = input.split('\n');
  const bars = inputs[1].split(' ').sort().reverse();
  const sides = [];
  let current = 0;
  for (let bar of bars) {
    if (bar === current) continue;
    current = bar;

    const n = bars.filter((b) => bar === b).length;
    if (n >= 4) {
      sides.push(bar);
      sides.push(bar);
      break;
    } else if (n >= 2 && (n != 1 || n != 3)) {
      sides.push(bar);
    }
    if (sides.length === 2) {
      break;
    }
  }
  if (sides.length === 2) {
    console.log(sides[0] * sides[1]);
  } else {
    console.log(0);
  }
}

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