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