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 Ruby (2.3.3) (judge verdict: Accepted)

# https://atcoder.jp/contests/abc150/tasks/abc150_c

def init_fact(n)
  @fact = Array.new(n + 1)
  @fact[0] = 1
  n.times { |i| @fact[i + 1] = @fact[i] * (i + 1) }
end

def order(ps)
  order2((1..ps.size).to_a, ps)
end

def order2(as, ps)
  return 0 if as.size == 0
  i = ps[0]
  ret = as.index(i) * @fact[as.size - 1]
  as.delete(i)
  ps.delete(i)
  ret + order2(as, ps)
end

N = gets.to_i
Ps = gets.split.map(&:to_i)
Qs = gets.split.map(&:to_i)

init_fact(N)
a = order(Ps)
b = order(Qs)
puts (a - b).abs