#include <iostream>
#include <fstream>
#include <cstring>
#include <vector>
#include <algorithm>

using namespace std;

string filename = "";

ifstream fin(filename + ".in");
ofstream fout(filename + ".out");

const int NMAX = 1e5;

vector<int> adj[NMAX + 5],gt[NMAX + 5];
vector<int> postordine;
int nr;
vector<int> ctc[NMAX + 5];

bool visited[NMAX + 5];

void dfs(int nod)
{

    visited[nod] = true;
    for(auto it : adj[nod])
        if(!visited[it])
            dfs(it);
    postordine.push_back(nod);
}

void dfst(int nod)
{

    visited[nod] = true;
    for(auto it : gt[nod])
        if(!visited[it])
            dfst(it);
    ctc[nr].push_back(nod);
}

int main()
{
    int n,m;
    fin>>n>>m;
    for(int i=1;i<=m;i++)
    {
        int u,v;
        fin>>u>>v;
        adj[u].push_back(v);
        gt[v].push_back(u);
    }
    for(int i=1;i<=n;i++)
    {
        if(!visited[i])
            dfs(i);
    }
    for(int i=1;i<=n;i++)
        visited[i]=false;
    reverse(postordine.begin(),postordine.end());
    for(auto it : postordine)
    {
        if(!visited[it])
        {
            nr++;
            dfst(it);
        }
    }
    fout<<nr<<'\n';
    for(int i=1;i<=nr;i++)
    {
        for(auto it : ctc[i])
            fout<<it<<' ';
        fout<<'\n';
    }
    return 0;
}