#include <queue>
#include <stack>
#include<stdio.h>
#include<iostream>
using namespace std;
 
int n,m,v[100000],nrdf[100000],inst[100000];
vector<int> l[100000]; 
int c,ndf,pozc=0;;
 
struct Muchie{
       int i,j;
} ;
 
stack<int> s;
 
vector<int> comp;
 
void bloc(int x,int tata){
	int u;
	s.push(x);
		ndf++;
		nrdf[x]=ndf;
		v[x]=ndf;
		inst[x]=1;
		for(int t=0;t<l[x].size();t++){
		        int j=l[x][t];
				if(nrdf[j]==0){

			 
					bloc(j,x);
				
					if(v[x]>v[j])
						v[x]=v[j];	
				}
				else
					if(inst[j]){
						if(v[x]>nrdf[j])
							v[x]=nrdf[j];	
					}
          }	
		 	
		  if (v[x] == nrdf[x]) {
		        do {
		            u = s.top();
					comp.push_back(u);
		            s.pop();
		            inst[u]=0;
		            //cout<<u+1;
		        }
		        while (u != x);
		        //cout<<endl;
		        c++;
		       comp.push_back(-1);
		}
	
	}
void bloc(){
		int i;
		c=0;
		for(i=0;i<n;i++){
			v[i]=0;
			nrdf[i]=0;
		
		}	
		for(i=0;i<n;i++)
			if(nrdf[i]==0)
				bloc(i,-1);
	}
	
int main(){
   
     FILE *f;
     int i,x,y,nrc=0,j;
       
     f=fopen("ctc.in","r");
     fscanf(f,"%d %d",&n,&m);
     for(i=0;i<m;i++){
         fscanf(f,"%d %d",&x,&y);
         l[x-1].push_back(y-1);
         //l[y-1].push_back(x-1);
     }
     fclose(f);
   
    
     bloc();             
                 
     f=fopen("ctc.out","w");
     fprintf(f,"%d",c);
   
          fprintf(f,"\n",c); 
          for(j=0;j<comp.size();j++){
                if(comp[j]>=0)
                   fprintf(f,"%d ",comp[j]+1);               
                else
                    fprintf(f,"\n");
          }
            
        
     fclose(f); 
     /*for(i=0;i<n;i++)
     	cout<<nrdf[i]<<" ";
     cout<<endl;
	 for(i=0;i<n;i++)
     	cout<<v[i]<<" ";
     cout<<endl;	*/
     
     return 0;   
}