Evirir#include <bits/stdc++.h>
using namespace std;

bool visited[2222];
vector<int> adj[2222];
int maxlevel=1;

void DFS(int now,int level){
    if(visited[now])    return;
    else visited[now]=true;
    maxlevel=max(maxlevel,level);
    for(int i=0;i<adj[now].size();i++){
        int x=adj[now][i];
        DFS(x,level+1);
    }
}

int main()
{
    int V;
    vector<int> boss;   //people who don't have a manager
    cin>>V;

    for(int i=0;i<V;i++){
        int j;
        cin>>j;
        if(j==-1)
            boss.push_back(i);
        else{
            adj[j-1].push_back(i);
        }
    }

    for(int i=0;i<boss.size();i++)
        DFS(boss[i],1);
    cout<<maxlevel;
    return 0;
}