CF1140A.Detective Book

Ivan recently bought a detective book. The book is so interesting that each page of this book introduces some sort of a mystery, which will be explained later. The $i$-th page contains some mystery that will be explained on page $a_i$ ($a_i \ge i$).

Ivan wants to read the whole book. Each day, he reads the first page he didn't read earlier, and continues to read the following pages one by one, until all the mysteries he read about are explained and clear to him (Ivan stops if there does not exist any page $i$ such that Ivan already has read it, but hasn't read page $a_i$). After that, he closes the book and continues to read it on the following day from the next page.

How many days will it take to read the whole book?

伊万最近买了一本侦探小说。这本书非常有趣，每一页都会引出某种谜题，而该谜题会在后续某页中得到解释。第 $i$ 页引入的谜题将在第 $a_i$ 页得到解释（满足 $a_i \ge i$）。

伊万希望完整地读完这本书。每天，他从自己尚未阅读的第一页开始阅读，并按顺序逐页继续阅读，直到他所读到的所有谜题都已被解释、对他而言完全清晰为止（即：不存在任何页面 $i$，使得伊万已经读过第 $i$ 页，但尚未读过第 $a_i$ 页；此时他便会停止阅读）。之后，他合上书本，并于次日从下一页继续阅读。

问：读完整本书共需要多少天？

The first line contains single integer $n$ ($1 \le n \le 10^4$) — the number of pages in the book.

The second line contains $n$ integers $a_1, a_2, \dots, a_n$ ($i \le a_i \le n$), where $a_i$ is the number of page which contains the explanation of the mystery on page $i$.

第一行包含一个整数 $n$（$1 \le n \le 10^4$）—— 表示书的页数。

第二行包含 $n$ 个整数 $a_1, a_2, \dots, a_n$（满足 $i \le a_i \le n$），其中 $a_i$ 表示第 $i$ 页上的谜题解释所在的页码。

Print one integer — the number of days it will take to read the whole book.

输出一个整数——读完整本书所需的天数。

Explanation of the example test:

During the first day Ivan will read only the first page. During the second day Ivan will read pages number $2$ and $3$. During the third day — pages $4$-$8$. During the fourth (and the last) day Ivan will read remaining page number $9$.

示例测试的解释：

第一天，伊万只阅读第一页；
第二天，伊万阅读第 $2$ 页和第 $3$ 页；
第三天，伊万阅读第 $4$–$8$ 页；
第四天（也是最后一天），伊万阅读剩余的第 $9$ 页。