Problem:
Score : 700 points

Problem Statement

We have N cards numbered 1, 2, ..., N.
Card i (1 \leq i \leq N) has an integer A_i written in red ink on one side and an integer B_i written in blue ink on the other side.
Initially, these cards are arranged from left to right in the order from Card 1 to Card N, with the red numbers facing up.

Determine whether it is possible to have a non-decreasing sequence facing up from left to right (that is, for each i (1 \leq i \leq N - 1), the integer facing up on the (i+1)-th card from the left is not less than the integer facing up on the i-th card from the left) by repeating the operation below. If the answer is yes, find the minimum number of operations required to achieve it.

Choose an integer i (1 \leq i \leq N - 1).
Swap the i-th and (i+1)-th cards from the left, then flip these two cards.

Constraints

1 \leq N \leq 18

1 \leq A_i, B_i \leq 50 (1 \leq i \leq N)

All values in input are integers.

Input

Input is given from Standard Input in the following format:

N
A_1 A_2 ... A_N
B_1 B_2 ... B_N

Output

If it is impossible to have a non-decreasing sequence, print -1.
If it is possible, print the minimum number of operations required to achieve it.

Sample Input 1

3
3 4 3
3 2 3

Sample Output 1

1

By doing the operation once with i = 1, we have a sequence [2, 3, 3] facing up, which is non-decreasing.

Sample Input 2

2
2 1
1 2

Sample Output 2

-1

After any number of operations, we have the sequence [2, 1] facing up, which is not non-decreasing.

Sample Input 3

4
1 2 3 4
5 6 7 8

Sample Output 3

0

No operation may be required.

Sample Input 4

5
28 15 22 43 31
20 22 43 33 32

Sample Output 4

-1

Sample Input 5

5
4 46 6 38 43
33 15 18 27 37

Sample Output 5

3

Solution in PHP7 (7.0.15) (judge verdict: Accepted)

<?php
$N = intval(trim(fgets(STDIN)));
$A = array_map("intval", explode(" ", trim(fgets(STDIN))));
$B = array_map("intval", explode(" ", trim(fgets(STDIN))));
$dp = array_fill(0, 1<<$N, array_fill(0,51,PHP_INT_MAX));
$dp[0][0] = 0;
for($bit = 0, $NN = (1<<$N); $bit < $NN; ++$bit){
    $con = 0;
    for ($i = 0; $i < $N; ++$i) if ($bit & (1<<$i)) ++$con;
    $ords = [];
    $iter = $con;
    for($i = 0; $i < $N; ++$i)
        if(!($bit & (1<<$i)))
            $ords[$i] = $iter++;
    for($s = 0; $s <= 50; ++$s){
        if($dp[$bit][$s] == PHP_INT_MAX)continue;
        foreach($ords as $p0 => $p1){
            $ns = ($p0-$con) & 1 ? $B[$p0] : $A[$p0];
            if($ns >= $s){
                $dp[$bit | (1<<$p0)][$ns] = min($dp[$bit|(1<<$p0)][$ns], $dp[$bit][$s] + abs($p1 - $con));
            }
        }
    }
}
$min = min($dp[(1<<$N)-1]);
if($min == PHP_INT_MAX){
    echo -1;
}else{
    echo $min;
}