#include <bits/stdc++.h>
using namespace std;
const int N = 2e5;
vector<int> g[N];
int deg[N];
int cnt[N];
void dfs(int v, int &l) {
  for (int i = 0; i < g[v].size(); i++) {
    cnt[g[v][i]] = l + 1;
    l++;
    dfs(g[v][i], l);
    l--;
  }
}
int main() {
  ios_base::sync_with_stdio(), cout.tie(NULL), cin.tie(NULL);
  ;
  int n;
  cin >> n;
  for (int i = 1; i <= n; i++) {
    cin >> deg[i];
    if (deg[i] != -1) {
      g[deg[i]].push_back(i);
    }
  }
  int ans = 1;
  for (int i = 1; i <= n; i++) {
    if (deg[i] == -1) {
      int level = 1;
      dfs(i, level);
    }
  }
  for (int i = 1; i <= n; i++) {
    ans = max(ans, cnt[i]);
  }
  cout << ans << endl;
}
