#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
using ll = long long; using mint=modint998244353; using ld = long double; 
const ll infl = 1LL << 60;
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }
const vector<int> dx = {1, 0, -1, 0}; const vector<int> dy = {0, 1, 0, -1};
template<typename T> using vc = vector<T>; template<typename T> using vvc = vc<vc<T>>; template<typename T> using vvvc = vc<vvc<T>>;
using vi = vc<int>;  using vvi = vvc<int>; using vl = vc<ll>; using vvl = vvc<ll>; using vvvl = vvc<vl>; using vvvvl = vvc<vvl>;
using vs = vc<string>; using vvs = vvc<string>; using P = pair<ll, ll>;
#define nrep(i,n) for (ll i = 0; i < (n); ++i)
#define nfor(i,s,n) for(ll i=s;i<n;i++)//i=s,s+1...n-1 ノーマルfor
#define vc_cout(v){ll n = v.size();nrep(i,n)cout<<v[i]<<" \n"[i+1==n];}//一次元配列を出力する
#define vv_cout(v){ll n = v.size();nrep(i,n){nrep(j,v[i].size()){cout<<v[i][j]<<' ';}cout<<endl;}}//二次元配列を出力する
template<class T> using pq = priority_queue<T, vc<T>>;//★大きい順に取り出す コスト,頂点 bfs系で使う　小さい順じゃないですABC305E
template<class T> using pq_g = priority_queue<T, vc<T>, greater<T>>;//小さい順に取り出す　ダイクストラ法で使う
#define cout(n) cout<<n<<endl;
ll N, M;
vl dist;
vvl g;

void dfs(ll v, ll p, ll d = 0) {
    dist[v] = d;
    for (auto to : g[v]) {
        if (to == p) continue; // Avoid going back to the parent node
        dfs(to, v, d + 1);
    }
    return;
}

int main() {
    cin.tie(nullptr);
    ios_base::sync_with_stdio(false);
    cin >> N;
    dist.resize(N+1, infl);
    g.resize(N+1);
    set<ll> s;
    nrep(i, N){
        ll x;
        cin >> x;
        if(x == 0) continue;
        g[i+1].push_back(x);
        g[x].push_back(i+1);
        s.insert(x);
    }
    vl roots;
    for (ll i = 1; i <= N; ++i) {
        if (s.find(i) == s.end()) {
            roots.push_back(i);
            dist[i] = 0;
            dfs(i, -1, 0);
        }
    }
    ll ans = 0;
    nfor(i, 1, N+1) {
        ans += (dist[i]==2);
    }
    cout(ans);
    // vc_cout(dist);
    return 0;
}