#include <bits/stdc++.h>
using namespace std ;
const int maxn = 1e5 + 5;
vector <int> g[maxn] ;
int n[maxn] ;
int dis[maxn] ;
bool mark[maxn];
int b = 0 , c = 0;

void bfs(int u){
  mark[u] = true ;
  queue <int> q ;
  q.push(u) ;
  dis[u] = 0 ;
  while (!q.empty()){
    int v = q.front();
    for (auto w : g[v]){
      if (!mark[w]){
        mark[w] = true ;
        q.push(w) ;
        dis[w] = dis[v] + 1 ;
        if (dis[w] > b ){
          b = dis[w];
        }
      }
    }
    q.pop() ;
  }
}

int main (){
  int t , m ;
  cin >> t ;
  int a[t] ;
  for (int i = 0 ; i < t ; i++){
    cin >> a[i] ;
    if (a[i] == -1){
      n[c] = i ;
      c++ ;
    }
    m = a[i] ;
    g[i].push_back(m) ;
    g[m].push_back(i) ;
  }
  for (int i = 0 ; i < c ; i++){
    bfs(n[i]) ;
  }
  cout << b ; 
}