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

int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    int n;
    cin >> n;
    vector<int> p(n);
    vector<bool> used(n, false);
    for(int i = 0; i < n; i++){
        cin >> p[i];
        p[i]--;
        if(p[i] == -1) continue;
        used[p[i]] = true;
    }
    int ans = 0;
    vector<bool> B(n);
    for(int i = 0; i < n; i++){
        if(used[i]) continue;
        if(p[i] == -1) continue;
        if(p[p[i]] == -1) continue;
        B[p[p[i]]] = true;
    }
    cout << count(B.begin(), B.end(), true) << '\n';
}