#include <iostream>
#include <queue>
#include <algorithm>
#include <vector>
//#include <gtest/gtest.h>

using std::vector;
using std::queue;

class Node;

class Node {
public:
	int key;
	Node *parent;
	vector<Node *> children;

	Node() {
		this->parent = NULL;
	}

	void setParent(Node *theParent) {
		parent = theParent;
		parent->children.push_back(this);
	}
};

int treeLevelCounter(vector<Node> &nodes, int rootIndex) {
	int levelCounter = 1;
	queue<Node *> q;
	int popCount = 0;
	int childrenCount = nodes[rootIndex].children.size();
	int grandChildrenCount = 0;
	for (int i = 0; i < childrenCount; i++) {
		q.push(nodes[rootIndex].children[i]);
	}
	while (!q.empty()) {
		if (popCount < childrenCount) {
			Node *n = q.front();
			q.pop();
			int i = n->children.size();
			if (i != 0) {
				for (int j = 0; j < i; j++) {
					q.push(n->children[j]);
				}
			}
			grandChildrenCount = grandChildrenCount + i;
			popCount = popCount + 1;
		} else {
			popCount = 0;
			childrenCount = grandChildrenCount;
			grandChildrenCount = 0;
			levelCounter = levelCounter + 1;
		}
	}
	return levelCounter + 1;
}
int getHeight(vector<int> &a) {
	vector<Node> nodes;
	nodes.resize(a.size());
	int rootIndex = 0;
	for (size_t i = 0; i < a.size(); i++) {
		int parentIndex = a[i];
		if (parentIndex == -1) {
			rootIndex = i;
		} else {
			nodes[i].setParent(&nodes[parentIndex]);
		}
	}
	return treeLevelCounter(nodes, rootIndex);
}

//TEST(GetTreeHeight, t1) {
//    vector<int> a = {4, -1, 4, 1, 1};
//    ASSERT_EQ(3, getHeight(a));
//}
//
//TEST(GetTreeHeight, t2) {
//    vector<int> a = {-1, 0, 4, 0, 3};
//    ASSERT_EQ(4, getHeight(a));
//}
//
//TEST(GetTreeHeight, t3) {
//    vector<int> a = {9, 7, 5, 5, 2, 9, 9, 9, 2, -1};
//    ASSERT_EQ(4, getHeight(a));
//}
//
//TEST(GetTreeHeight, t4) {
//    vector<int> a = {8, 8, 5, 6, 7, 3, 1, 6, -1, 5};
//    ASSERT_EQ(6, getHeight(a));
//}

int main() {
	size_t an;
	std::cin >> an;
	vector<int> a(an);
	for (size_t i = 0; i < an; i++) {
		std::cin >> a[i];
	}
	std::cout << getHeight(a) << std::endl;
}