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 n = inputs[0];
  const bars = inputs[1].split(' ').sort().reverse();
  
  const sides = [];
  const vert = [];
  const hori = [];
  for (let i = 0; i < bars.length; i++) {
    if (sides.length === 2) break;
    
    const bar1 = bars[i];
    const bar2 = bars[i + 1] ? bars[i + 1] : null;
    const bar3 = bars[i + 2] ? bars[i + 2] : null;
    const bar4 = bars[i + 3] ? bars[i + 3] : null;
    if (bar1 === bar2) {
      vert.push(bar1);
    }
    if (bar3 === bar4) {
      hori.push(bar3);
    }
  }
  if (sides.length === 2) {
    console.log(vert[0] * hori[0]);
  } else {
    console.log(0);
  }
}

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