#include <bits/stdc++.h>
using namespace std;
int n, p[3000], k, m = 0, c;
int main() {
  cin >> n;
  for (int i = 1; i <= n; i++) cin >> p[i];
  for (int i = 1; i <= n; i++) {
    k = p[i];
    c = 1;
    while (k > 0) {
      c++;
      k = p[k];
    }
    m = max(c, m);
  }
  cout << m;
  return 0;
}
