#include <iostream>
#include <fstream>
#include <vector>
#define O 100005
using namespace std;

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

vector<vector<int> > G, GT, CTC;
short viz[O];
int TS[O];
int N, M, k, nrCTC;

void citire()
{
    in >> N >> M;
    G.resize(N + 2);
    GT.resize(N + 2);
    CTC.resize(N + 2);
    int x, y;
    for(int i = 1; i <= M; i++)
    {
        in >> x >> y;
        G[x].push_back(y);
        GT[y].push_back(x);
    }
}

void DFS1(int z)
{
    viz[z] = 1;
    for(int i = 0; i < G[z].size(); i++)
    {
        int Vecin = G[z][i];
        if(!viz[Vecin])
            DFS1(Vecin);
    }
    TS[++k] = z;
}

void DFS2(int z)
{
    viz[z] = 2;
    CTC[nrCTC].push_back(z);
    for(int i = 0; i < GT[z].size(); i++)
    {
        int Vecin = GT[z][i];
        if(viz[Vecin] == 1)
            DFS2(Vecin);
    }
}

int main()
{
    citire();
    for(int i = 1; i <= N; i++)
        if(!viz[i])
            DFS1(i);

    for(int i = N; i >= 1; i--)
    {
        if(viz[TS[i]] == 1)
        {
            nrCTC++;
            DFS2(TS[i]);
        }
    }

    out << nrCTC << '\n';

    for(int i = 1; i <= nrCTC; i++)
    {
        for(int j = 0; j < CTC[i].size(); j++)
            out << CTC[i][j] << ' ';
        out << '\n';
    }

}