#include <fstream>
#include <vector>
#define MX 100001
using namespace std;

ifstream fin("ctc.in");
ofstream fout("ctc.out");
int n,m;
vector<int> v[MX], S, vt[MX], traseu;
bool viz[MX];

void citire()
{
    int i,j;
    int x,y;
    fin>>n>>m;
    for(i=1; i<=m; i++)
    {
        fin>>x>>y;
        v[x].push_back(y);
    }
}

void DFS(int i)
{
    viz[i] = 1;
    vector<int>::iterator it;
    for(it=v[i].begin(); it!=v[i].end(); it++)
    {
        if(viz[*it] == 0)
        {
            DFS(*it);
        }
    }

    S.push_back(i);
}

void DFST(int i)
{
    viz[i] = 1;
    traseu.push_back(i);
    vector<int>::iterator it;
    for(it=vt[i].begin(); it!=vt[i].end(); it++)
    {
        if(viz[*it] == 0)
        {
            DFST(*it);
        }
    }
}

void ctc()
{
    vector<int>::iterator it;
    int i, nr=0;
    for(i=1; i<=n; i++)
    {
        if(viz[i] == 0)
        {
            DFS(i);
        }
    }

    for(i=1; i<=n; i++) //graful transpus
    {
        for(it=v[i].begin(); it!=v[i].end(); it++)
        {
            vt[*it].push_back(i);
        }

        v[i].clear();
        viz[i] = 0;
    }

    while(!S.empty())
    {
        i = S.back();
        S.pop_back();
        if(viz[i] == 1) continue;
        DFST(i);
        traseu.push_back(0);
        nr++;
    }

    for(i=1; i<=n; i++)
    {
        vt[i].clear();
    }

    fout<<nr<<'\n';
    for(it=traseu.begin(); it!=traseu.end(); it++)
    {
        if(*it == 0)
        {
            fout<<'\n';
        }
        else
        {
            fout<<*it<<' ';
        }
    }
    traseu.clear();
}

int main()
{
    citire();
    ctc();

    fin.close(); fout.close();
    return 0;
}