#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
#define ll long long
#define rep(i,a,b) for(int i=(a);i<(b);i++)
#define repl(i,a,b) for(ll i=(a);i<(b);i++)
#define all(a) (a).begin(),(a).end()

template <typename T> bool chmin(T &a,T b){if(a>b){a=b;return true;} return false;}
template <typename T> bool chmax(T &a,T b){if(a<b){a=b;return true;} return false;}

int main(){
  int n; cin >> n;
  vector<bool> ch(n,false);
  vector<int> p(n);
  rep(i,0,n){
    cin >> p[i];
    p[i]--;
    if(p[i] != -1) ch[p[i]]=true;
  }
  vector<bool> flag(n,false);
  int ans=0;
  rep(i,0,n){
    if(ch[i]) continue;
    int now=i;
    int num=0;
    while(p[now] != -1 && num<=2){
      now=p[now];
      num++;
      if(num == 2){
        if(flag[now]) break;
        ans++;
        flag[now]=true;
      }
    }
  }

  cout << ans << endl;
}