A.Party

import heapq, math
from itertools import *
from bisect import *
from collections import *
from sys import stdin, stdout


###########-> Templates <- ##########
def pr(out):
    return stdout.write(f"{out}\n")


def input():
    return stdin.readline().rstrip()


def int_inp():
    return int(input())


def inp_int_l():
    return list(map(int, stdin.readline().split()))


def inp_l():
    return stdin.readline().split()


####################################


def solve():
    n = int(input())
    graph = [[] for _ in range(n)]
    indegree = [0] * n
    for node in range(n):
        p = int_inp()
        if p != -1:
            graph[p - 1].append(node)
            indegree[node] += 1
    level = [[node for node in range(n) if indegree[node] == 0]]
    queue = deque(level[0])
    while queue:

        lev = []
        for _ in range(len(queue)):
            node = queue.popleft()
            for nei in graph[node]:
                lev.append(nei)
                queue.append(nei)
        level.append(lev)
    count = 0
    for l in level:
        if l:
            count += 1

    print(count)


if __name__ == "__main__":
    t = 1
    for _ in range(t):
        solve()