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

int N, M, x, y, nrc;
vector <int> G[100005], CTC[100005], tsrt, T[100005];
bitset < 100005 > viz;

void dfs(int nod)
{
    viz[nod]=1;
    vector<int>::iterator it=G[nod].begin();
    for (; it!=G[nod].end(); ++it)
        if (!viz[*it]) dfs(*it);
    tsrt.push_back(nod);
}

void dfs2(int nod)
{
    viz[nod]=0; CTC[nrc].push_back(nod);
    vector<int>::iterator it=T[nod].begin();
    for (; it!=T[nod].end(); ++it)
        if (viz[*it]) dfs2(*it);
}

int main()
{
    f>>N>>M;
    for (int i=1; i<=M; ++i)
        f>>x>>y, G[x].push_back(y), T[y].push_back(x);

    for (int i=1; i<=N; ++i)
        if (!viz[i]) dfs(i);
    for (int i=tsrt.size()-1; i>=0; --i)
        if (viz[tsrt[i]]) ++nrc, dfs2(tsrt[i]);

    g<<nrc<<'\n';
    for (int i=1; i<=nrc; ++i)
    {
        for (int j=0; j<(int)CTC[i].size(); ++j)
            g<<CTC[i][j]<<' '; g<<'\n';
    }
    return 0;
}