#include <fstream>
#include <string.h>
#include <vector>

#define maxN 25072

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


int use[maxN];
int st[maxN];

vector <int> g[maxN];
vector <int> gt[maxN];
vector <int> ctc[maxN];

int sol=0;

inline void dfs(int nod)
{
        use[nod]=1;
        for(int i=0;i<g[nod].size();++i)
                if(!use[g[nod][i]]) dfs(g[nod][i]);

        st[++st[0]]=nod;
}

inline void dfst(int nod)
{
        use[nod]=1;
        for(int i=0;i<gt[nod].size();++i)
                if(!use[gt[nod][i]]) dfst(gt[nod][i]);

        ctc[sol].push_back(nod);
}

int main(int argc,char *argv[])
{
        int M,N,x,y;

        fin>>N>>M;

        for(int i=1;i<=M;++i)
        {
                fin>>x>>y;
                g[x].push_back(y);
                gt[y].push_back(x);
        }

        memset(st,0,sizeof(st));
        memset(use,0,sizeof(use));

        for(int i=1;i<=N;++i)
                if(!use[i]) dfs(i);

        memset(use,0,sizeof(use));

        for(int i=N;i>0;--i)
                if(!use[st[i]])
        {
                ++sol;
                dfst(st[i]);
        }

        fout<<sol<<'\n';
        for(int i=1;i<=sol;++i)
        {
                for(int j=0;j<ctc[i].size();++j)
                        fout<<ctc[i][j]<<" ";
                fout<<'\n';
        }

        return 0;
}