Problem:
Score : 200 points

Problem Statement

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

Output

Print the number of the friendly pairs.

Sample Input 1

4
2 1 4 3

Sample Output 1

2

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

Sample Input 2

3
2 3 1

Sample Output 2

0

There are no friendly pairs.

Sample Input 3

5
5 5 5 5 1

Sample Output 3

1

There is one friendly pair: (1，5).

Solution in C++14 (GCC 5.4.1) (judge verdict: Wrong Answer)


#include <string>
#include <fstream>
#include <streambuf>
#include <iostream>
using namespace std;

int main(int argc, const char * argv[]) {
    int n;
    cin>>n;
    
    int *arr=new int[n]();
    for (int i=0; i<n; i++) {
        cin>>arr[i];
    }
    
    int count=0;
    for (int i=0; i<n; i++) {
        if (arr[arr[i]]==i) {
            count++;
        }
    }
    delete arr;
    
    cout<<count<<endl;
   
    return 0;
}