#639

#include <iostream>
#include <fstream>

using namespace std;

ifstream f("inaltime.in");
ofstream g("inaltime.out");

int a[101][101],q[101],t[101],viz[101],poz,n,mx;

void BFS(int start)
{
    int p,u;
    p=u=1;
    q[1]=start;
    viz[start]=1;
    while(p<=u)
    {
        int x=q[p++];
        for(int i=1;i<=n;i++)
            if(a[x][i] and viz[i]==0)
            {
                q[++u]=i;
                viz[i]=viz[x]+1;
                if(viz[i]>mx)
                    mx=viz[i];
            }
    }
}

void citire()
{
    int i;
    f>>n;
    for(i=1;i<=n;i++)
    {
        f>>t[i];
        if(t[i]==0)
            poz=i;
        a[i][t[i]]=a[t[i]][i]=1;
    }
}

int main()
{
    int i,x;
    citire();
    BFS(poz);
    g<<mx;
    return 0;
}