The brave Knight came to the King and asked permission to marry the princess.
The King knew that the Knight was brave, but he also wanted to know if he was smart enough. So he asked him to solve the following task.
There is a permutation of numbers from to . You can make two types of operations.
Swap and , and , ..., and .
Swap and , and , ..., and .
The task is to find the minimal number of operations required to sort the given permutation.
The Knight was not that smart actually, but quite charming, so the princess asks you to help him to solve the King's task.
输入格式
The first line contains the integer (). The second line contains integers --- the permutation of numbers from 1 to .
输出格式
Print one integer --- the minimal number of operations required to sort the permutation. If it is impossible to sort the permutation using these operations, print .
样例
样例输入 1
3
6 3 2 5 4 1
样例输出 1
3
样例输入 2
2
3 4 2 1
样例输出 2
-1
样例输入 3
4
1 2 3 4 5 6 7 8
样例输出 3
0
数据范围与提示
In the first example, you can sort the permutation in three operations:
