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

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

const int NMAX = 1e5 + 5;
const char nl = '\n';

vector<int> g[NMAX], invers[NMAX], componente[NMAX];
stack<int> order;
int visitat[NMAX];

void dfs(int nod) {
    visitat[nod] = 1;
    for (auto neigh: invers[nod]) {
        if (visitat[neigh] == 0) {
            dfs(neigh);
        }
    }
    order.push(nod);
}

void dfs2(int nod, int nivel) {
    visitat[nod] = 1;
    for (auto neigh: g[nod]) {
        if (visitat[neigh] == 0) {
            dfs2(neigh, nivel);
        }
    }
   componente[nivel].push_back(nod);
}

int main () {
    int n, m, x, y;
    fin >> n >> m;
    for (int i = 0; i < m; i++) {
        fin >> x >> y;
        g[x].push_back(y);
        invers[y].push_back(x);
    }
    for (int i = 1; i <= n; i++) {
        visitat[i] = 0;
    }
    for (int i = 1; i <= n; i++) {
        if (visitat[i] == 0) {
            dfs(i);

        }
    }
    for (int i = 1; i <= n; i++) {
        visitat[i] = 0;
    }
    int nivel = -1;
    while (!order.empty()) {
        int nod = order.top();
        order.pop();
        if (visitat[nod] == 0) {
            nivel++;
            dfs2(nod, nivel);
        }
    }

    fout << ++nivel << nl;
    for (auto it: componente) {
        for (auto nod: it) {
            fout << nod << " ";
        }
        fout << nl;
    }
}