#include <bits/stdc++.h>
using namespace std;

int main(){
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);

    int N; cin >> N;
    vector<int> P(N);
    for(auto &p : P) cin >> p,p--;

    vector<bool> root(N,true);
    vector<vector<int>> Graph(N);
    for(int i=0; i<N; i++){
        if(P.at(i) == -1) continue;
        root.at(P.at(i)) = false;
        Graph.at(i).push_back(P.at(i));

    }

    set<int> S;
    for(int i=0; i<N; i++) if(root.at(i)){
        if(P.at(i) == -1) continue;
        int to = P.at(P.at(i));
        if(to == -1) continue;
        S.insert(to);

    }
    cout << S.size() << endl;
}