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

using namespace std;

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

vector <int> G1[nmax], G2[nmax];
int n, m, x, y, viz2[nmax], viz1[nmax * 2], st[nmax], k = 1, nr_el, j = 1;

void read(){
    fin >> n >> m;
    for(int i = 1; i <= m; ++i){
        fin >> x >> y;
        G1[x].push_back(y);
        G2[y].push_back(x);
    }
}

void DFS1(int nod){
    viz1[nod] = 1;
    for(int i = 0; i < G1[nod].size(); ++i)
        if(!viz1[G1[nod][i]])
            DFS1(G1[nod][i]);
    st[k] = nod;
    k++;
}

void DFS(int nod){
    viz1[j] = nod;
    j++;
    viz2[nod] = 1;
    for(int i = 0; i < G2[nod].size(); ++i)
        if(!viz2[G2[nod][i]])
            DFS(G2[nod][i]);
}

void kosaraju(){
    for(int i = k - 1; i > 0; --i){
        if(viz2[st[i]] == 0){
            nr_el++;
            DFS(st[i]);
        }
        viz1[j++] = -1;
    }
    fout << nr_el << endl;
    int c = 0;
    for(int i = 1; i < j; i++){
        if(viz1[i] == -1 && c == 0){
            fout << endl;
            c = 1;
        }
        else if(viz1[i] != -1){
            fout << viz1[i] << " ";
            c = 0;
        }
    }
}

int main(){
    read();
    for(int i = 1; i <= n; ++i)
        if(viz1[i] == 0)
            DFS1(i);
    kosaraju();
    fin.close();
    fout.close();
    return 0;
}