tree_len

# Input
n = int(input())
s = [int(x) for x in input().rstrip().split()]

# Init
mas_len = [0] * n
mas_len[s.index(-1)] = -1
lst = []

# Main
for i in range(n):
    if mas_len[i] != 0:
        continue
    lst.append(i)
    cur = s[i]
    while cur != -1:
        if mas_len[cur] != 0:
            break
        lst.append(cur)
        cur = s[cur]
    for j in range(len(lst)):
        tmp = lst.pop()
        if mas_len[cur] == -1:
            mas_len[tmp] = mas_len[cur] + j + 3
        else:
            mas_len[tmp] = mas_len[cur] + j + 1

# Output
# print(mas_len)
if max(mas_len) == -1:
    print('1')
else:
    print(max(mas_len))