#include <bits/stdc++.h>
using namespace std;
const int maxn = 2000;
int pre[maxn];
int countlen(int i) {
  int ans = 0, p;
  for (p = i; p != -2; p = pre[p]) ans++;
  return ans;
}
int main() {
  int i, n;
  cin >> n;
  for (i = 0; i < n; i++) cin >> pre[i], pre[i]--;
  int ans = 0;
  for (i = 0; i < n; i++) ans = max(ans, countlen(i));
  cout << ans << endl;
  return 0;
}
