Problem:
Score : 300 points

Problem Statement

We have two permutations P and Q of size N (that is, P and Q are both rearrangements of (1,~2,~...,~N)).

There are N! possible permutations of size N. Among them, let P and Q be the a-th and b-th lexicographically smallest permutations, respectively. Find |a - b|.

Notes

For two sequences X and Y, X is said to be lexicographically smaller than Y if and only if there exists an integer k such that X_i = Y_i~(1 \leq i < k) and X_k < Y_k.

Constraints

2 \leq N \leq 8

P and Q are permutations of size N.

Input

Input is given from Standard Input in the following format:

N
P_1 P_2 ... P_N
Q_1 Q_2 ... Q_N

Output

Print |a - b|.

Sample Input 1

3
1 3 2
3 1 2

Sample Output 1

3

There are 6 permutations of size 3: (1,~2,~3), (1,~3,~2), (2,~1,~3), (2,~3,~1), (3,~1,~2), and (3,~2,~1). Among them, (1,~3,~2) and (3,~1,~2) come 2-nd and 5-th in lexicographical order, so the answer is |2 - 5| = 3.

Sample Input 2

8
7 3 5 4 2 1 6 8
3 8 2 5 4 6 7 1

Sample Output 2

17517

Sample Input 3

3
1 2 3
1 2 3

Sample Output 3

0

Solution in Haskell (GHC 7.10.3) (judge verdict: Accepted)

import           Control.Exception (assert)
import           Data.List         (permutations, sort)

main :: IO ()
main = do
  n <- readLn
  p <- map read . words <$> getLine
  q <- map read . words <$> getLine
  assert (length p == n && length q == n) $
    print $ solve n p q

solve :: Int -> [Int] -> [Int] -> Int
solve n p q
  | p < q     = solve' n p q
  | otherwise = solve' n q p

solve' :: Int -> [Int] -> [Int] -> Int
solve' n p q = length $ takeWhile (q /=) $ dropWhile (p /=) $ allPermutation n

allPermutation :: Int -> [[Int]]
allPermutation n = sort $ permutations [1..n]