#include <iostream>
#include <fstream>
#include <vector>
#include <cstring>
#define nmax 100005

using namespace std;

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

int n, m, timp, nrComp;
int final[nmax], ordin[nmax];
bool viz[nmax];
vector <int> G[nmax], GT[nmax], SOL[nmax];

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

void DF_Final(int nod) {
    viz[nod] = true;
    for (int i = 0; i < G[nod].size(); i++)
        if(!viz[G[nod][i]])
            DF_Final(G[nod][i]);
    timp++;
    final[nod] = timp;
}

void DF(int nod) {
    viz[nod] = true;
    for (int i = 0; i < GT[nod].size(); i++)
    if (!viz[GT[nod][i]])
        SOL[nrComp].push_back(GT[nod][i]),
        DF(GT[nod][i]);
}

void solve() {
    for (int i = 1; i <= n; i++)
        if (!viz[i])
            DF_Final(i);
    for (int i = 1; i <= n; i++)
        ordin[n - final[i] + 1] = i;
    memset(viz, false, sizeof(viz));
    for (int i = 1; i <= n; i++) {
        int k = ordin[i];
        if (!viz[k]){
            nrComp++;
            SOL[nrComp].push_back(k);
            DF(k);
        }
    }
    fout << nrComp << "\n";
    for (int i = 1; i <= nrComp; i++) {
        for (int j = 0; j < SOL[i].size(); j++)
            fout << SOL[i][j] << " ";
        fout << "\n";
    }
}

int main() {

    citire();
    solve();

    fin.close();
    fout.close();

    return 0;
}