#include <iostream>
#include <set>

#define pb push_back
#define mp make_pair
#define mod 1000000007

#define rep(i,n) for(int i=0;i<n;i++)
#define reps(i,a,b) for(int i=a;i<=b;i++)
#define rev(i,a,b) for(int i=a;i>=b;i--)

using namespace std;
typedef long long ll;
typedef long double ld;

class Task
{
public:
    const int mod2=1000000;
    set<int>a[2222];
    void solve(istream& in,ostream& out)
    {
        int n;
        in>>n;
        int c;

        reps(i,1,n)
        {
            in>>c;
            if(c!=-1)
            {
                a[c].insert(i);
            }
        }

        done(n);

        int res=1;

        for(int i=1;i<=n;i++)
        {
            for(auto h=a[i].begin();h!=a[i].end();h++)
            {
                out<<(*h)<<" ";
            }

            if(a[i].size()!=0)
            {
                out<<endl;
            }
        }

        set<int>store;

        for(int i=1;i<=n;i++)
        {
            store.insert(i);
        }

        set<int>repeat;
        for(int i=1;i<=n;i++)
        {
            if(a[i].size()!=0)
            {
                repeat.insert(i);
                store.erase(i);
                for(auto h=store.begin();h!=store.end();h++)
                {
                     if(a[i].find(*h)==a[i].end() && (*h)!=i)
                     {
                         repeat.insert(*h);
                         store.erase(*h);
                     }
                }

                if(repeat.size()!=0)
                {
                     res++;
                     repeat.clear();
                }
            }
        }

        out<<res<<endl;
    }

    void done(int n)
    {
        for(int i=1;i<=n;i++)
        {
            if(a[i].size()!=0)
            {
                for(auto j=a[i].begin();j!=a[i].end();j++)
                {
                    if(a[*j].size()!=0)
                    {
                        for(auto h=a[*j].begin();h!=a[*j].end();h++)
                        {
                            a[i].insert(*h);
                        }
                    }
                }
            }
        }
    }
};


int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    cout.tie(NULL);
    Task solver;
    istream& in(std::cin);
    ostream& out(std::cout);
    solver.solve(in,out);
    out.flush();

    return 0;
}