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

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

const int nmax = 1e5+5;
vector <int> g[nmax], ctc[nmax];
stack <int> st;
bitset <nmax> viz;
int lev[nmax], low[nmax], ind=1, nr;

void tarjan(int dad)
{
    vector <int> :: iterator son;
    int nod;
    low[dad]=lev[dad]=ind++;
    st.push(dad);
    viz[dad]=true;
    for(son=g[dad].begin(); son!=g[dad].end(); son++)
    {
        if(lev[*son]==false)
        {
            tarjan(*son);
            low[dad]=min(low[dad], low[*son]);
        }
        else if(viz[*son]==true)
            low[dad]=min(low[dad], low[*son]);
    }
    if(low[dad]==lev[dad])
    {
        nr++;
        do {
            nod=st.top();
            st.pop();
            viz[nod]=false;
            ctc[nr].push_back(nod);
        } while(nod!=dad);
    }
}
int main()
{
    ios_base::sync_with_stdio(false);
    vector <int> :: iterator it;
    int n, m, i, x, y;
    fin >> n >> m;
    for(i=1; i<=m; i++)
    {
        fin >> x >> y;
        g[x].push_back(y);
    }

    for(i=1; i<=n; i++)
        if(lev[i]==0) tarjan(i);

    fout << nr << "\n";
    for(i=1; i<=nr; i++)
    {
        for(it=ctc[i].begin(); it!=ctc[i].end(); it++)
            fout << *it << " ";
        fout << "\n";
    }
    fin.close();
    fout.close();
    return 0;
}