#include <bits/stdc++.h>
using namespace std;
int main() {
  int i, x, ans, num, n, fa[2001];
  while (scanf("%d", &n) != EOF) {
    for (i = 1; i <= n; i++) {
      scanf("%d", &fa[i]);
    }
    ans = 1;
    for (i = 1; i <= n; i++) {
      num = 1;
      x = i;
      while (fa[x] != -1) {
        num++;
        x = fa[x];
      }
      if (num > ans) ans = num;
    }
    printf("%d\n", ans);
  }
  return 0;
}
