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 Java7 (OpenJDK 1.7.0) (judge verdict: Wrong Answer)

import java.io.IOException;
import java.util.Scanner;

public class Main {
	public static void main(String[] args) throws IOException {
		Scanner scanner = new Scanner(System.in);
		int num = scanner.nextInt();
		int[] array = new int[num];
		int count = 0;
		for (int i = 1; i < num + 1; i++) {
			if (scanner.hasNextInt()) {
				int a = scanner.nextInt();
				array[i - 1] = a;
				if (i > a) {
					if (array[a - 1] == i) count++;
				}
			}
		}
		scanner.close();
		for (int i = 0; i < num; i++) {
			System.out.print(array[i]);
		}
		System.out.println(count);
	}
}