Subordinates

题意翻译

一家公司有 $n$ 个人，其中，第 $s$ 个人是主任。 除了主任，每个人都有且仅有一个直接上司，上司下属关系构成一棵树。 每个人被要求回答他的上司数目 $a_i$，但他们可能会记错。 问记错自己上司数目的人至少有几个。 $1 \le n\le 2\times 10^5,1\le s\le n,0\le a_i\le n-1$

题目描述

There are $ n $ workers in a company, each of them has a unique id from $ 1 $ to $ n $ . Exaclty one of them is a chief, his id is $ s $ . Each worker except the chief has exactly one immediate superior. There was a request to each of the workers to tell how how many superiors (not only immediate). Worker's superiors are his immediate superior, the immediate superior of the his immediate superior, and so on. For example, if there are three workers in the company, from which the first is the chief, the second worker's immediate superior is the first, the third worker's immediate superior is the second, then the third worker has two superiors, one of them is immediate and one not immediate. The chief is a superior to all the workers except himself. Some of the workers were in a hurry and made a mistake. You are to find the minimum number of workers that could make a mistake.

输入输出格式

输入格式

The first line contains two positive integers $ n $ and $ s $ ( $ 1<=n<=2·10^{5} $ , $ 1<=s<=n $ ) — the number of workers and the id of the chief. The second line contains $ n $ integers $ a_{1},a_{2},...,a_{n} $ ( $ 0<=a_{i}<=n-1 $ ), where $ a_{i} $ is the number of superiors (not only immediate) the worker with id $ i $ reported about.

输出格式

Print the minimum number of workers that could make a mistake.

输入输出样例

输入样例 #1

3 2
2 0 2

输出样例 #1

1

输入样例 #2

5 3
1 0 0 4 1

输出样例 #2

2

说明

In the first example it is possible that only the first worker made a mistake. Then: - the immediate superior of the first worker is the second worker, - the immediate superior of the third worker is the first worker, - the second worker is the chief.