#include <bits/stdc++.h>
using namespace std;
#define int long long int
#define endl "\n"

signed main(){
    ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
    int n;cin>>n;
    vector<int> p(n+1),idg(n+1,0);
    for(int i=1;i<=n;i++){
        cin>>p[i];
        if(p[i] != 0)idg[p[i]]++;
    }
    unordered_set<int> s;
    for(int i=1;i<=n;i++){
        if(idg[i]!=0)continue;
        int x = p[i];
        if(x==0)continue;
        int y = p[x];
        if(y==0)continue;
        s.insert(i);
    }
    cout<<s.size();
    return 0;
}