#include <iostream>
#include <fstream>
#include <vector>
#include <stack>
#define NLIM 100001

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

int viz[NLIM];
vector<int> Muchii[NLIM], MuchiiT[NLIM], Conex[NLIM];
stack<int> Topo;

void citire(int &n, int &m) {
    f >> n >> m;
    for(int i=1; i<=m; i++) {
        int s, d;
        f >> s >> d;
        Muchii[s].push_back(d);
        MuchiiT[d].push_back(s);
    }
}

void DFS(int nod, bool transpose = false, int conex = -1) {
    viz[nod] = transpose ? 2 : 1;
    if(transpose) Conex[conex].push_back(nod);

    for(int i=0; i<(transpose ? Muchii : MuchiiT)[nod].size(); i++) {
        int vecin = (transpose ? Muchii : MuchiiT)[nod][i];
        if(!viz[vecin] && ! transpose)
            DFS(vecin);
        else if(viz[vecin] == 1 && transpose) {
            DFS(vecin, transpose, conex);
        }
    }

    if(!transpose) Topo.push(nod);
}

int Kosoraju(int n) {
    int conex = 0;

    for(int i=1; i<=n; i++)
        if(!viz[i])
            DFS(i);

    while(!Topo.empty()) {
        int top = Topo.top();
        Topo.pop();

        if(viz[top] == 1) {
            conex++;
            DFS(top, true, conex);
        }
    }

    return conex;
}

int main() {
    int n, m, ctc;

    citire(n, m);
    ctc = Kosoraju(n);

    g << ctc << '\n';
    for(int i=1; i<=ctc; i++) {
        for (int j = 0; j < Conex[i].size(); j++)
            g << Conex[i][j] << ' ';
        g << '\n';
    }

    return 0;
}