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: Accepted)

        import java.util.*;
         
        public class Main {
         
        	public static void main(String[] args){
            		Scanner in = new Scanner(System.in);
            		
            		int numbers = in.nextInt();
            		ArrayList<Integer> array = new ArrayList<Integer>();
            		for (int x = 0; x < numbers; x++){
            			array.add(in.nextInt());
            		}
            		
            		int counter = 0;
            		for (int x = 0; x < array.size(); x++){
            			if (x + 1 == array.get(array.get(x)-1)){
            				counter++;
            			}
            		}
            		counter /= 2;
            		System.out.println(counter);
            		in.close();
            }
        }