#include <algorithm>
#include <iostream>
#include <vector>
#if defined(__unix__) || defined(__APPLE__)
#endif

class Node;

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

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

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

    int height(Node node)
    {
        if (node.children.size() == 0)
            return 0;

        int maxH = 0;
        for (int i = 0; i < node.children.size(); ++i)
        {
            if (maxH < height(*node.children[i]))
            {
                maxH = height(*node.children[i]);
            }
        }
        maxH += 1;
        return maxH;
    }
};


int main()
{
    std::ios_base::sync_with_stdio(0);
    int n;
    std::cin >> n;
    int root;

    std::vector<Node> nodes;
    nodes.resize(n);
    for (int child_index = 0; child_index < n; child_index++) {
        int parent_index;
        std::cin >> parent_index;
        if (parent_index >= 0)
            nodes[child_index].setParent(&nodes[parent_index]);
        else
        {
            //нужно отловить корень
            root = child_index;
        }
        nodes[child_index].key = child_index;
    }
    std::cout << nodes[root].height(nodes[root]) + 1 << std::endl;
    //for (int i =0; i < n; ++i)
    //{
    //    for (int j = 0; j < nodes[i].children.size(); ++j)
    //    {
    //        std::cout << nodes[i].children[j];
    //    }
    //    std::cout  << std::endl;
    //}
    return 0;
}