#include <iostream>
#include <fstream>
#include <vector>

using namespace std;

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

#define lim 100010
int viz[lim], id[lim], minm[lim], nr, st[lim], dr, n, m;
vector <vector <int>> rez;
vector <int> G[lim];


void tarjan (int nod)
{
    id[nod]=minm[nod]=++nr;
    viz[nod]=1;
    st[++dr] = nod;
    for (auto it:G[nod])
    {
        if (!id[it]) tarjan(it);
        if (viz[it]) minm[nod] = min (minm[nod], minm[it]);
    }
    if (minm[nod] == id[nod])
    {
        vector <int> ans;
        while (st[dr] != nod)
        {
            ans.push_back(st[dr]);
            viz[st[dr]]=0;
            dr--;
        }
        ans.push_back(st[dr]);
        viz[st[dr]]=0;
        dr--;
        rez.push_back(ans);
    }
}

int main()
{
    int x,y;
    fin>>n>>m;
    for (int i=1; i<=m; i++)
    {
        fin>>x>>y;
        G[x].push_back(y);
    }

    for (int i=1; i<=n; i++)
        if (!id[i])    tarjan (i);

    fout<<rez.size()<<'\n';
    for (auto it:rez)
    {
        for(auto itt:it)
            fout<<itt<<' ';
        fout<<'\n';
    }

    fout.close();
    return 0;
}