#include <iostream>
#include <stack>
#include <vector>
#include <fstream>
using namespace std;

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

vector <int> L[50002];
vector <int> G[50002];
vector < vector <int> > CTC_solution;
stack <int> stiva;
vector <int> componenta;

bool viz1[50002];
bool viz2[50002];
int n, m;

/// Eu trebuie sa scot

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

void DFS_1(int k)
{
    int j, nod;
    viz1[k] = 1;
    for (j = 0; j < L[k].size(); j++)
    {
        nod = L[k][j];
        if (!viz1[nod])
            DFS_1(nod);
    }
    stiva.push(k);
}

void DFS_2(int k)
{
    int j, nod;
    viz2[k] = 1;
    cout << k << endl;
    for (j = 0; j < G[k].size(); j++)
    {
        nod = G[k][j];
        if (!viz2[nod])
            DFS_2(nod);
    }
    componenta.push_back(k);
}


void Rezolva()
{
    int i, j, nod;
    for (i = 1; i <= n; i++)
        if (!viz1[i])
            DFS_1(i);

    while (!stiva.empty())
    {
            componenta.clear();
            nod = stiva.top();
            stiva.pop();
            if (!viz2[nod])
            {
                DFS_2(nod);
                CTC_solution.push_back(componenta);
            }
    }
}


void Afisare()
{
    /// cout << "Im here mofackeeeeers";
    int i, j;
    fout << CTC_solution.size() << "\n";
    for (i = 0; i < CTC_solution.size(); i++)
    {
        for (j = 0; j < CTC_solution[i].size()-1; j++)
        {
            fout << CTC_solution[i][j] << " ";
        }
        fout << CTC_solution[i][CTC_solution[i].size()-1];
        fout << "\n";
    }
}

int main ()
{
    int i;
    Citire();
    Rezolva();
    Afisare();
    return 0;
}