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: Runtime Error)

{-# LANGUAGE CPP #-}
#define MOD (1000000007 :: Integer)
import Prelude hiding (mod)

mod :: Integer -> Integer -> Integer
mod x y
  | x >= y    = mod (x - y) y
  | otherwise = x

calc' :: String -> Integer
calc' [x] = 3
calc' [x,y] = 6
calc' (x:y:xs)
  | x == y  = 6 * calc (x:y:xs)
  | x /= y  = 3 * calc (x:y:xs)

calc :: String -> Integer 
calc [x,y]
  | x == y = 1
  | x /= y = 2
calc [x,y,z]
  | x == y    = 1
  | y == z    = 2
  | otherwise = 4
calc (x:y:z:w:xs)
  | x == y && z == w  = (3 * calc(z:w:xs)) `mod` MOD
  | x == y && z /= w  = calc(z:w:xs) `mod` MOD
  | x /= y            = (2 * calc(y:z:w:xs)) `mod` MOD

main :: IO ()
main = do
  getLine
  str <- getLine
  getLine
  putStrLn . show . calc' $ str