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 Haskell (GHC 7.10.3) (judge verdict: Accepted)

{-# OPTIONS_GHC -O #-}

import Control.Monad
import Data.List
import Data.Ord
import qualified Data.ByteString.Lazy.Char8 as B

readIntLL :: IO [[Int]]
readIntLL = map(unfoldr(B.readInt.B.dropWhile(==' '))).B.lines<$>B.getContents

rsort = sortBy $ flip compare

ts [] = [0,0]
ts (_:[]) = [0,0]
ts (a:b:as)
    | a == b = a : (ts as)
    | True = ts (b:as)

main=do
    n:as <- readIntLL
    print $ product $ take 2 $ ts $ rsort $ head as