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

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

int n, m;
int timp = 0, nrComp = 0;
int final[nmax], ordin[nmax];
vector <int> G[nmax], GT[nmax];
stack <int> sol[nmax];
bool vizF[nmax], viz[nmax];

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

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

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

void solve() {
    int i, k;

    for (i = 1; i <= n; i++)
        if (!vizF[i])
            DF_Final(i);
    
    for (i = 1; i <= n; i++)
        ordin[n - final[i] + 1] = i;
    
    for (i = 1; i <= n; i++) {
        k = ordin[i];
        if (!viz[k]) {
            nrComp++;
            sol[nrComp].push(k);
            DF(k);
        }
    }
    
    fout << nrComp << "\n";
    for (i = 1; i <= nrComp; i++) {
        while (!sol[i].empty()) {
            fout << sol[i].top() << " ";
            sol[i].pop();
        }
        fout << "\n";
    }
    
}

int main() {
    readData();
    solve();
    fin.close();
    fout.close();
    return 0;
}