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

int main() {
    cin.tie(nullptr);
    ios_base::sync_with_stdio(false);
    
    int N;
    cin >> N;
    vector<int> P(N);
    rep(i, 0, N) {
        cin >> P[i];
        --P[i];
    }
    
    vector<bool> ok(N, true);
    rep(i, 0, N) if (P[i] != -1) ok[P[i]] = false;
    
    vector<bool> check(N, false);
    rep(q, 0, N) if (ok[q]) {
        int p = P[q];
        if (p != -1) {
            int i = P[p];
            if (i != -1) check[i] = true;
        }
    }
    
    int ans = 0;
    rep(i, 0, N) if (check[i]) ++ans;
    cout << ans << '\n';
}