#include <iostream>
#include <fstream>
#include <vector>
#include <stack>

using namespace std;

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

const int NMAX = 100000 + 1;

int n, m;
vector <int> graf[NMAX];

int ind_crt;
int ind[NMAX];
int lowlink[NMAX];
bool in_stack[NMAX];

stack <int> stiva;

vector < vector <int> > componente;

void citeste() {
    f >> n >> m;

    int a, b;
    for (int i = 1; i <= m; i++) {
        f >> a >> b;
        graf[a].push_back(b);
    }
}

void DFS(int nod) {
    if (ind[nod]) return;

    ind_crt++;
    ind[nod] = lowlink[nod] = ind_crt;
    in_stack[nod] = true;
    stiva.push(nod);

    int l, fiu;
    l = graf[nod].size();

    for (int i = 0; i < l; i++) {
        fiu = graf[nod][i];

        DFS(fiu);
        if (!in_stack[fiu]) continue;
        lowlink[nod] = min(lowlink[fiu], ind[nod]);
    }

    if (lowlink[nod] != ind[nod]) return;

    vector <int> componenta_curenta;

    int top;
    do {
        top = stiva.top();
        stiva.pop();
        in_stack[top] = false;
        componenta_curenta.push_back(top);
    } while (top != nod);

    componente.push_back(componenta_curenta);
}

void scrie() {
    int l1, l2;

    l1 = componente.size();
    g <<l1 << '\n';
    for (int i = 0; i < l1; i++) {
        l2 = componente[i].size();
        for (int j = 0; j < l2; j++) g <<componente[i][j] << ' ';
        g <<'\n';
    }
}

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

int main() {
    citeste();
    rezolva();
    scrie();

    return 0;
}