#include <cstdio>
#include <vector>
#include <cstring>
#define MAXN 100000
using namespace std;
vector <int> G[MAXN+1];
vector <int> V[MAXN+1];
vector <int> R[MAXN+1];
int top[MAXN+1];
char viz[MAXN+1];
int pos=0,con;
void Sort_Top(int nod){
    viz[nod]=1;
    for(int i=0;i<G[nod].size();i++)
     if(viz[G[nod][i]]==0)
        Sort_Top(G[nod][i]);
    top[pos++]=nod;
}
void DFS(int nod){
    viz[nod]=1;
    R[con].push_back(nod);
    for(int i=0;i<V[nod].size();i++)
     if(viz[V[nod][i]]==0)
        DFS(V[nod][i]);
}
int main(){
    FILE*fi,*fout;
    int i,n,m,x,y,j;
    fi=fopen("ctc.in" ,"r");
    fout=fopen("ctc.out" ,"w");
    fscanf(fi,"%d%d" ,&n,&m);
    for(i=0;i<m;i++){
        fscanf(fi,"%d%d" ,&x,&y);
        G[x].push_back(y);
        V[y].push_back(x);
    }
    for(i=1;i<=n;i++)
     if(viz[i]==0)
      Sort_Top(i);
    memset(viz,0,sizeof(viz));
    con=1;
    for(i=n-1;i>=0;i--)
     if(viz[top[i]]==0){
       DFS(top[i]);
       con++;
     }
    fprintf(fout,"%d\n" ,con-1);
    for(i=1;i<con;i++){
       for(j=0;j<R[i].size();j++)
         fprintf(fout,"%d " ,R[i][j]);
       fprintf(fout,"\n");
    }
    fclose(fi);
    fclose(fout);
    return 0;
}