#include <bits/stdc++.h>
using namespace std;
const long long mod = 1e9 + 7;
vector<long long int> graph[100007];
long long int vis[100007];
long long int mxm;
void dfs(long long int u, long long int p, long long int d) {
  vis[u] = 1;
  mxm = max(mxm, d);
  for (long long int v : graph[u]) {
    dfs(v, u, d + 1);
  }
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  ;
  long long int tc = 1;
  long long int cs = 0;
  while (tc--) {
    long long int n;
    cin >> n;
    mxm = 0;
    for (long long int i = 1; i <= n; i++) {
      long long int a;
      cin >> a;
      if (a != -1) graph[a].push_back(i);
    }
    long long int ans = 0;
    for (long long int i = 1; i <= n; i++) {
      if (!vis[i]) {
        dfs(i, -1, 1);
        ans = max(ans, mxm);
        mxm = 0;
      }
    }
    cout << ans << '\n';
  }
  return 0;
}
