#include <iostream>
#include <fstream>
#include <vector>
using namespace std;

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

#define NMAX 100005

vector <int> g[NMAX];

int i, m, n, a[NMAX], viz[NMAX], onStack[NMAX], id, low[NMAX], poz, x, y ,st[NMAX], vf, k, rasp[NMAX];

void dfs(int nod)
{
    id++;
    viz[nod]=low[nod]=id;
    onStack[nod]=1;
    vf++;
    st[vf]=nod;
    for(unsigned int i=0; i<g[nod].size(); i++)
    {
        int curr=g[nod][i];
        if(!viz[curr])
            dfs(curr);
        if(onStack[curr])
            low[nod]=min(low[nod],low[curr]);
    }
    if(low[nod]==viz[nod])
    {
        poz++;
        while(st[vf+1]!=nod && vf>=0)
        {
            k++;
            a[k]=st[vf];
            low[st[vf]]=low[nod];
            onStack[st[vf]]=0;
            vf--;
        }
        rasp[poz]=k;
    }
}

int main()
{
    fin>>n>>m;
    for(i=1; i<=m; i++)
    {
        fin>>x>>y;
        g[x].push_back(y);
    }
    id=0;
    for(i=1; i<=n; i++)
    {
        if(viz[i]==0)
        {
            dfs(i);
        }
    }
    fout<<poz<<'\n';
    k=0;
    for(i=1; i<=poz; i++)
    {
        while(k<rasp[i])
        {
            k++;
            fout<<a[k]<<" ";
        }
        fout<<'\n';
    }
    return 0;
}