#include <bits/stdc++.h>
using namespace std;
#define ALL(x) (x).begin(), (x).end()
#define REP(i, n) for(ll i=0; i<(ll)(n); i++)

template<typename T> bool chmax(T& a, T b) { return a<b ? a=b, true : false; }
template<typename T> bool chmin(T& a, T b) { return a>b ? a=b, true : false; }
using ll=long long; const int INF=1e9+10; const ll INFL=4e18;
using VI=vector<int>; using VVI=vector<VI>; using VL=vector<ll>; using VVL=vector<VL>;
using PL=pair<ll,ll>; using VP=vector<PL>; using WG=vector<vector<pair<int,ll>>>;

#ifdef LOCAL
#include "./debug.hpp"
#else
#define debug(...)
#define print_line
#endif


//----------------------------------------------------------

void solve() {
    ll N; cin>>N;
    VL P(N); REP(i,N) cin>>P[i], P[i]--;

    VL indeg(N);
    REP(i,N) if(P[i]!=-1) indeg[P[i]]++;

    set<ll> st;
    REP(i,N) if(indeg[i]==0) {
        ll p=P[i];
        if(p!=-1) {
            ll q=P[p];
            if(q!=-1) st.insert(q);
        }
    }

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

int main() {
    ios::sync_with_stdio(false); cin.tie(nullptr);
    //cout<<fixed<<setprecision(15);
    int T=1;
    //cin>>T;
    while(T--) solve();
}