#include<fstream>
#include<vector>
using namespace std;
ifstream in("ctc.in");
ofstream out("ctc.out");

#define N 100001

vector <int> lista[N], comp[N], transp[N];

int n, m, ct=0;
int viz[N]={0}, post[N];

void citire()
{
    int x, y;
    in >> n >> m;
    for(int i=1; i<=m; i++)
    {
        in >> x >> y;
        lista[x].push_back(y);
        transp[y].push_back(x);
    }
}

void Dfs(int nod)
{
    viz[nod] = 1;
    for(int i=0; i<lista[nod].size(); i++)
        if(viz[lista[nod][i]] == 0)
            Dfs( lista[nod][i] );
    post[++ct] = nod;
}

void TDfs(int nod)
{
    viz[nod]=0;
    comp[ct].push_back(nod);
    for(int i=0; i<transp[nod].size(); i++)
        if(viz[transp[nod][i]] == 1)
            TDfs( transp[nod][i] );
}

int main ()
{
    citire();
    for(int i=1; i<=n; i++)
        if(viz[i] == 0)
            Dfs(i);

    ct=0;
    for(int i=n; i>=1; i--)
        if(viz[post[i]] == 1)
        {
            ct++;
            TDfs(post[i]);
        }

    out<<ct<<'\n';
    for(int i=1; i<=ct; i++)
    {
        for(int j=0; j<comp[i].size(); j++)
            out<<comp[i][j]<<' ';
        out<<'\n';
    }

    return 0;
}