#define F first
#define S second
#define PB push_back
#define PF push_front
#define pF pop_front
#define pB pop_back
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef vector<int> vi;
typedef vector<char> vc;
typedef pair<int, int> pi;
typedef deque<int> di;
typedef deque<char> dc;
typedef vector<string> vs;
vector<bool> used(2001, false); int best = 1; int depth = 1;
vector<vector <int> > l(2001, vector<int> (0));
int dfs(int v){
    used[v] = true;
    for (auto u : l[v]){
        if (!used[u]){
            depth++;
            dfs(u);
        }
    }
    best = max(best, depth);
    depth--;
}
int n;
int main(){
    ios::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    cin >> n; int x;
    for (int i = 1; i < n + 1; ++i){
        cin >> x;
        if (x != -1){
            l[x].PB(i);
        }
    }
    for (int i = 1; i < n + 1; ++i){
        dfs(i);
        for (int j = 1; j < n + 1; ++j)
            used[j] = false;
        depth = 1;
    }
    cout << best;
}