#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<int64_t>> children;
int64_t dfs(int64_t root){
    if (children[root].empty()){
        return 1;
    }
    int64_t temp = 0;
    for (auto x : children[root]) {
         temp = max(dfs(x) + 1, temp);
    }
    return temp;
}
int main() {
    int64_t n = readInt();
//    cin >> n;
    children.resize(n);
    int64_t root = -1;
    for (int64_t i = 0; i < n; i++){
        int64_t temp = readInt();
//        cin >> temp;
        if (temp == -1){
            root = i;
            continue;
        }
        children[temp].push_back(i);
    }
    writeInt(dfs(root));
}