#include <iostream>
#include <vector>
#include <fstream>

using namespace std;

    ifstream fin("ctc.in");
    ofstream fout("ctc.out");

vector <int> G[100005];
vector <int> Gi[100005];
vector <int> Go[100005];
vector <int> discovered;
vector <bool> used;
vector <int> where;
int n,m;

void DFP(const int n, vector<int>*G)
{
    used[n]=true;

    vector<int>::iterator it;

    for(it=G[n].begin();it!=G[n].end();it++)
        if(used[*it]==false)
            DFP(*it,G);

    discovered.push_back(n);

}

void DFM(const int n, vector<int>*G, const int which)
{
    vector<int>::iterator it;

    where[n]=which;

    for(it=G[n].begin();it!=G[n].end();it++)
        if(where[*it]==-1)
            DFM(*it,G,which);

}


int main()
{
    int x,y;

    fin>>n>>m;

    for(int i=1;i<=m;i++)
    {
        fin>>x>>y;
        Go[x].push_back(y);
        Gi[y].push_back(x);
    }

    used.resize(n+1,0);
    where.resize(n+1,-1);
    where.assign(n+1,-1);

    for(int i=0;i<n;i++)
        if(used[i]==false)
            DFP(i,Go);

    int coun=0;

    for(;discovered.size();discovered.pop_back())
        if(where[discovered.back()]==-1)
        {
            DFM(discovered.back(),Gi,coun);
            coun++;
        }

    for(int i=0;i<n;i++)
        G[where[i]].push_back(i);

    fout<< coun-1<<'\n';

    vector<int>::const_iterator it;

    for(int i=0;i<coun-1;i++)
    {
        for(it=G[i].begin();it!=G[i].end();it++)
            fout<<*it<<' ';
        fout<<'\n';
    }
}