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# Uses python3
import queue
class Node(object):
def __init__(self, key):
self._key = key
self.children = []
@property
def key(self):
return self._key
@key.setter
def key(self, key):
self._key = key
def add_child(self, child):
self.children.extend([child])
def get_children(self):
return self.children
def tree_level_counter(nodes, root_index):
level_counter = 1
q = queue.Queue()
pop_count = 0
child_count = len(nodes[root_index].get_children())
grand_children_count = 0
for i in range(child_count):
q.put(nodes[root_index].get_children()[i])
while not q.empty():
if pop_count < child_count:
node = q.get()
i = len(node.get_children())
if i != 0:
for j in range(i):
q.put(node.get_children()[j])
grand_children_count = grand_children_count + i
pop_count = pop_count + 1
else:
pop_count = 0
child_count = grand_children_count
grand_children_count = 0
level_counter = level_counter + 1
return level_counter + 1
def get_height(a):
# The code below has the bug of alias/referencing. Code after that fixed it.
# nodes = [Node(-5)] * len(a)
nodes = []
for i in range(len(a)):
nodes.append(Node(i))
root_index = 0
for i in range(len(a)):
parent_index = a[i]
nodes[i].key = i
if parent_index == -1:
root_index = i
else:
nodes[parent_index].add_child(nodes[i])
return tree_level_counter(nodes, root_index)
if __name__ == '__main__':
n = int(input())
parents = list(map(int, input().split()))
print(get_height(parents))
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