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 <iostream>
#include <string>

int main()
{
    int N = 0;
    std::cin >> N;
    int flag[N];
    int list[N];
    int count = 0;

    for(int i = 0; i < N; i++)
    {
        std::cin >> list[i];
        flag[i] = 0;
    }
    int index = 0;
    for(int i = 0; i < N; i++)
    {
        if (flag[i] == 0){
            index = list[i] - 1;
            if(flag[index] == 0 && list[index] == i)
            {
                count = count + 1;
                flag[index] = 1;
            }
        }
    }

    std::cout << count << '\n';
}