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

void dfs(int u,int &sz,vector<bool> &vis,vector<vector<int>> &adj){
    vis[u] = 1;
    sz++;
    for(auto &v:adj[u]){
        if(vis[v]==0)dfs(v,sz,vis,adj);
    }
}

signed main(){
    ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
    int n;cin>>n;
    vector<int> p(n);
    for(int i=0;i<n;i++)cin>>p[i];
    vector<vector<int>> adj(n+1);
    vector<int> c(n+1,0);
    for(int i=0;i<n;i++){
        if(p[i]==0)continue;
        c[p[i]]++;
        adj[i+1].push_back(p[i]);
        adj[p[i]].push_back(i+1);
    }
    queue<int> q;
    for(int i=1;i<=n;i++){
        if(c[i]==0)q.push(i);
    }
    vector<bool> v(n+1,0);
    vector<int> s;
    while(!q.empty()){
        int i = q.front();
        q.pop();
        if(v[i]==0){
            int sz=0;
            dfs(i,sz,v,adj);
            s.push_back(sz);
        }
    }
    int ans=0;
    for(int i=0;i<s.size();i++){
        if(s[i]>=3)ans++;
    }
    cout<<ans;
    return 0;
}