#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  int cnt = 0;
  for (int i = 1; i <= n; i++) {
    int a;
    cin >> a;
    if (a == i) cnt++;
  }
  cout << (cnt + 1) / 2 << endl;
}
