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: Accepted)


#include <stdio.h>

int main()
{
    int i,n,a[100000],count=0,k,j;
  scanf("%d\n",&n);
  
   for(i=1;i<=n;i++)
   {
       scanf("%d",&a[i]);
      
       
   }
   for(i=1;i<n;i++)
   {
       if(a[a[i]]==i)
       {
           count++;
           
           a[a[i]]=0;
       }
    
   }
    
   printf("%d\n",count);
    return 0;
}