Friendly Rabbits

AtCoder

IDcodefestival_2016_qualA_b

Time2000ms

Memory256MB

Difficulty—

There are $N$ rabbits, numbered $1$ through $N$. The $i$\-th ($1≤i≤N$) rabbit likes rabbit $a_i$. Note that no rabbit can like itself, that is, $a_i≠i$. For a pair of rabbits $i$ and $j$ ($i＜j$), we call the pair ($i，j$) a _friendly pair_ if the following condition is met. * Rabbit $i$ likes rabbit $j$ and rabbit $j$ likes rabbit $i$. Calculate the number of the friendly pairs. ## Constraints * $2≤N≤10^5$ * $1≤a_i≤N$ * $a_i≠i$ ## Input The input is given from Standard Input in the following format: $N$ $a_1$ $a_2$ $...$ $a_N$ [samples]

Samples

Input #1

4
2 1 4 3

Output #1

2

There are two friendly pairs: $(1，2)$ and $(3，4)$.

Input #2

3
2 3 1

Output #2

0

There are no friendly pairs.

Input #3

5
5 5 5 5 1

Output #3

1

There is one friendly pair: $(1，5)$.

API Response (JSON)

{
  "problem": {
    "name": "Friendly Rabbits",
    "description": {
      "content": "There are $N$ rabbits, numbered $1$ through $N$. The $i$\\-th ($1≤i≤N$) rabbit likes rabbit $a_i$. Note that no rabbit can like itself, that is, $a_i≠i$. For a pair of rabbits $i$ and $j$ ($i＜j$), we c",
      "description_type": "Markdown"
    },
    "platform": "AtCoder",
    "limit": {
      "time_limit": 2000,
      "memory_limit": 262144
    },
    "difficulty": "None",
    "is_remote": true,
    "is_sync": true,
    "sync_url": null,
    "sign": "codefestival_2016_qualA_b"
  },
  "statements": [
    {
      "statement_type": "Markdown",
      "content": "There are $N$ rabbits, numbered $1$ through $N$.\nThe $i$\\-th ($1≤i≤N$) rabbit likes rabbit $a_i$. Note that no rabbit can like itself, that is, $a_i≠i$.\nFor a pair of rabbits $i$ and $j$ ($i＜j$), we c...",
      "is_translate": false,
      "language": "English"
    }
  ]
}

Full JSON Raw Segments