#include <bits/stdc++.h>
using namespace std;
const long long mod = 1e9 + 7;
long long expo(long long x, long long y) {
  long long res = 1;
  while (y) {
    if (y % 2) res = (res * x % mod) % mod;
    x = (x * x) % mod;
    y /= 2;
  }
  return res;
}
long long inv(long long x) { return expo(x, mod - 2); }
long long add(long long x, long long y) { return (x + y) % mod; }
long long sub(long long x, long long y) { return (x - y) % mod; }
long long mul(long long x, long long y) {
  return ((x % mod) * (y % mod)) % mod;
}
void dfs(vector<vector<long long> > &a, vector<long long> &d, long long st,
         long long n) {
  stack<long long> s;
  s.push(st);
  d[st] = 1;
  vector<bool> v(n + 1, false);
  v[st] = true;
  while (!s.empty()) {
    long long x = s.top();
    s.pop();
    for (long long i = 0; i < a[x].size(); i++) {
      if (!v[a[x][i]]) {
        s.push(a[x][i]);
        v[a[x][i]] = true;
        d[a[x][i]] = d[x] + 1;
      }
    }
  }
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  long long n;
  cin >> n;
  vector<long long> p(n + 1, 0);
  vector<vector<long long> > a(n + 1);
  vector<long long> temp;
  for (long long i = 1; i <= n; i++) {
    cin >> p[i];
    if (p[i] == -1) {
      temp.push_back(i);
      continue;
    }
    a[i].push_back(p[i]);
    a[p[i]].push_back(i);
  }
  vector<long long> d(n + 1, 1);
  for (long long i = 0; i < temp.size(); i++) {
    dfs(a, d, temp[i], n);
  }
  long long ans = -1;
  for (long long i = 1; i < d.size(); i++) ans = max(d[i], ans);
  cout << ans;
  cout << "\n";
}
