#include <iostream>
#include <fstream>
#include <vector>
#include <stack>
#define nmax 50001
using namespace std;

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

vector<int> v[nmax], transpose[nmax], sol[nmax], components[nmax];
vector <int> topo;

bool seen[nmax];

int c, n, m;

void dfs(int x){
    seen[x] = true;
    for(int i=0; i<v[x].size(); i++)
        if(!seen[v[x][i]])
            dfs(v[x][i]);
    topo.push_back(x);
}

void kosajaru(int x){
    seen[x] = true;
    components[c].push_back(x);
    for(int i=0; i<transpose[x].size(); i++){
        if(!seen[transpose[x][i]])
            kosajaru(transpose[x][i]);
    }
}

int main(){
    int x, y, i;
    fin >> n >> m;
    for(int i=1; i<=m; i++){
        fin >> x >> y;
        v[x].push_back(y); // the adjency list
        transpose[y].push_back(x); // the transpose adjency list
    }
    for(int i=1; i<=n; i++)
        if(!seen[i])    dfs(i); // the first dfs on the original graph
    for(int i=1; i<=n; i++) seen[i] = false;

    for(i=n-1; i>=0; i--){
        if(!seen[topo[i]]){
            c++;
            kosajaru(topo[i]);
        }
    }
    fout << c << "\n";
    for(int i=1; i<=c; i++){
        for(int j=0; j<components[i].size(); j++)
            fout << components[i][j] << " ";
    fout << "\n";
    }
    return 0;
}