ICPC Asia Pacific Championship 2025 — K. Book Sorting
Problem K

Book Sorting

Time limit: 2 seconds

You have \(n\) books arranged from left to right on a bookshelf. These books are uniquely labeled from \(1\) to \(n\). The \(i\)-th book from the left is labeled \(p_i\). You want to sort the books so that their labels are in ascending order from left to right.

In one step, you can perform one of the following actions:

Compute the minimum number of steps required to sort the books.

Input

The first line of input contains an integer \(n\) (\(2 \le n \le 500\,000\)). The second line contains \(n\) pairwise distinct integers \(p_1, p_2, \ldots, p_n\) (\(1 \le p_i \le n\)).

Output

Output the minimum number of steps to sort the books in ascending order from left to right by their labels.

Sample Input #1
6
6 2 1 4 3 5
Sample Output #1
3

Explanation for the sample input/output #1

You can do the following three steps in order: swap the books labeled \(2\) and \(1\), swap the books labeled \(4\) and \(3\), and move the book labeled \(6\) to the rightmost position.

6 2 1 4 3 5 \(\rightarrow\) 6 1 2 4 3 5 \(\rightarrow\) 6 1 2 3 4 5 \(\rightarrow\) 1 2 3 4 5 6

It can be shown that two or fewer steps are insufficient to sort the books.

Sample Input #2
9
9 2 4 3 7 5 1 8 6
Sample Output #2
5