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 (GCC 5.4.1) (judge verdict: Wrong Answer)

main() {
	int i, N;
	scanf( "%d", &N );

	int A[N];
	int ct = 0;
	int checked[N];

	for( i=0; i<N; i++ ) { scanf( "%d", &A[i] ); checked[i] = 0; }

	for( i=0; i<N; i++ ) {
		if( checked[i] ) continue;
		if( A[ A[i] ] == i ){ ct++; checked[ A[i] ] = 1; }
	}

	printf( "%d\n", ct );
	return 0;
}