Takahashi's Secret

AtCoder

IDabc228_b

Time2000ms

Memory256MB

Difficulty—

Takahashi has $N$ friends. They have nicknames: Friend $1$, Friend $2$, $\ldots$, Friend $N$. One day, Takahashi accidentally let one of his friends, Friend $X$, learn his shameful secret. For each $i = 1, 2, \ldots, N$, when Friend $i$ learns the secret, he/she will share it with Friend $A_i$, if Friend $A_i$ has not already learned it. How many of Takahashi's friends will learn the secret in the end? ## Constraints * $2 \leq N \leq 10^5$ * $1 \leq X \leq N$ * $1 \leq A_i \leq N$ * $A_i \neq i$ * All values in input are integers. ## Input Input is given from Standard Input in the following format: $N$ $X$ $A_1$ $A_2$ $\cdots$ $A_N$ [samples]

Samples

Input #1

4 2
3 1 1 2

Output #1

3

Takahashi's secret will be learned by Friend $1$, Friend $2$, and Friend $3$, as follows.

*   One day, Takahashi let Friend $2$ learn the secret.
*   Friend $2$ shares it with Friend $1$.
*   Friend $1$ shares it with Friend $3$.

In the end, three of his friends learn the secret, so we print $3$.

Input #2

20 12
7 11 10 1 7 20 14 2 17 3 2 5 19 20 8 14 18 2 10 10

Output #2

API Response (JSON)

{
  "problem": {
    "name": "Takahashi's Secret",
    "description": {
      "content": "Takahashi has $N$ friends. They have nicknames: Friend $1$, Friend $2$, $\\ldots$, Friend $N$. One day, Takahashi accidentally let one of his friends, Friend $X$, learn his shameful secret.   For each ",
      "description_type": "Markdown"
    },
    "platform": "AtCoder",
    "limit": {
      "time_limit": 2000,
      "memory_limit": 262144
    },
    "difficulty": "None",
    "is_remote": true,
    "is_sync": true,
    "sync_url": null,
    "sign": "abc228_b"
  },
  "statements": [
    {
      "statement_type": "Markdown",
      "content": "Takahashi has $N$ friends. They have nicknames: Friend $1$, Friend $2$, $\\ldots$, Friend $N$.\nOne day, Takahashi accidentally let one of his friends, Friend $X$, learn his shameful secret.  \nFor each ...",
      "is_translate": false,
      "language": "English"
    }
  ]
}

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