#define _GLIBCXX_DEBUG 0
#include <iostream>
#include <cassert>
#include <algorithm>
#include <vector>
#include <unordered_map>
#include "optimization.h"
#include <map>

#define all(a) a.begin, a.end()
using namespace std;
vector<vector<int>> children;
int dfs(int root, int count){
    if (children[root].empty()){
        return count;
    }
    int temp = 0;
    for (auto x : children[root]){
        temp = max(dfs(x, count + 1), count);
    }
    count = max(temp, count);
    return count;
}
int main() {
    int n;
    cin >> n;
    children.resize(n);
    int root = -1;
    for (int i = 0; i < n; i++){
        int temp;
        cin >> temp;
        if (temp == -1){
            root = i;
            continue;
        }
        children[temp].push_back(i);
    }
    cout << dfs(root, 1);
}