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 Java8 (OpenJDK 1.8.0) (judge verdict: Wrong Answer)

import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int ni = sc.nextInt();
		int au[] = new int[ni];

		int nj =1;
		int tnum=0;

		au[0] =  sc.nextInt();

		for (int i=1; i < ni; i++){
			tnum = sc.nextInt();
			boolean flg = true;
			for (int j =0; j< nj; j++){
				if(tnum == au[j]){
					flg = false;
				}
			}
			if (flg){
				au[nj] = tnum;
				nj++;
			}

		}



		if (nj%2 == 0){
			System.out.println(nj/2);
		}else{
			System.out.println(0);
		}
		sc.close();
	}

}