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



void solve(){
    int N; cin >> N;
    vector<bool> ok(N, true);
    vector<int> P(N);
    for(int i = 0; i < N; ++i){
        cin >> P[i];
        --P[i];
        if(P[i] == -1) continue;
        ok[P[i]] = false;
    }
    int cnt = 0;
    vector<bool> re(N, true);
    for(int i = 0; i < N; ++i){
        if(ok[i]){
            int c = i;
            c = P[c];
            if(c == -1) continue;
            c = P[c];
            if(c == -1) continue;
            if(re[c]){
                ++cnt;
                re[c] = false;
            }
        }
    }
    cout << cnt << "\n";
}


int main(){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cout << setprecision(10) << fixed;


    int T;
    T = 1;
    //cin >> T;
    for(;T--;) solve();
}