#include <fstream>
#include <vector>
#include <stack>
#include <bitset>

using namespace std;

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

int n, m;
int nr_componente;
int viz[100005];
vector <int> graf[100005];
vector <int> graf_transpus[100005];
vector <int> sol[100005];
stack <int> a;

void citire()
{
    int x, y;
    fin >> n >> m;
    for(int i = 0; i < m; i++)
    {
        fin >> x >> y;
        graf[x].push_back(y);
        graf_transpus[y].push_back(x);
    }
}

void DFS(int i)
{
    viz[i] = 1;
    for(unsigned int j = 0; j < graf[i].size(); j++)
    {
        if(!viz[graf[i][j]])
        {
            viz[graf[i][j]] = 1;
            DFS(graf[i][j]);
        }
    }
    a.push(i);
}

void init_stack()
{
    for(int i = 1; i <= n; i++)
        if(!viz[i])
            DFS(i);
}

void DFS2(int i)
{
    viz[i] = 2;
    for(unsigned int j = 0; j < graf_transpus[i].size(); j++)
        if(viz[graf_transpus[i][j]] < 2)
        {
            viz[graf_transpus[i][j]] = 2;
            DFS2(graf_transpus[i][j]);
        }
    sol[nr_componente].push_back(i);
}


void solve()
{
    while(!a.empty())
    {
        int nod = a.top();
        a.pop();
        if(viz[nod] > 1)
            continue;
        nr_componente++;
        DFS2(nod);
    }
}

void afisare()
{
    fout << nr_componente << '\n';
    for(int i = 1; i <= nr_componente; i++)
    {
        for(auto &v : sol[i])
            fout << v << ' ';
        fout << '\n';
    }
}

int main()
{
    citire();
    init_stack();
    solve();
    afisare();
    return 0;
}