# include <fstream>
# include <vector>
# define DIM 100010
using namespace std;
ifstream fin("ctc.in");
ofstream fout("ctc.out");
vector <int> Lista[DIM],sol[DIM];
int poz[DIM],low[DIM],Marcat[DIM],s[DIM],n,m,u,x,y,i,j,r,nctc;
void tarjan(int nc){
    r++;
    poz[nc]=r;
    low[nc]=r;
    Marcat[nc]=1;
    s[++u]=nc;
    for(int i=0;i<Lista[nc].size();i++){
        int nv=Lista[nc][i];
        if(poz[nv]==0){
            tarjan(nv);
            low[nc]=min(low[nc],low[nv]);
        }
        else
            if(Marcat[nv])
                low[nc]=min(low[nc],low[nv]);
    }
    if(low[nc]==poz[nc]){
        nctc++;
        while(s[u]!=nc){
            Marcat[s[u]]=0;
            sol[nctc].push_back(s[u]);
            u--;
        }
        u--;
        sol[nctc].push_back(nc);
        Marcat[nc]=0;
    }
}
int main () {
    fin>>n>>m;
    for(i=1;i<=m;i++){
        fin>>x>>y;
        Lista[x].push_back(y);
    }
    for(i=1;i<=n;i++)
        if(poz[i]==0)
            tarjan(i);
    fout<<nctc<<"\n";
    for(i=1;i<=nctc;i++){
        for(j=0;j<sol[i].size();j++)
            fout<<sol[i][j]<<" ";
        fout<<"\n";
    }
    return 0;
}