#include<iostream>
#include<fstream>
#include<stack>
#include<vector>
#include<bitset>
using namespace std;
long n,id=1,ctc=0;
int vf=0,ids[100010],low[100010];
bitset <100010> peStiva;
stack <int> S;
vector <int> ve[100010],ct[100010];

void rezolvare();

int main(){
    ifstream f("ctc.in");
    int i,x,y,m; f>>n>>m;
    for(i=1;i<=m;i++){
        f>>x>>y;
        ve[x].push_back(y);
    }
    f.close();
    rezolvare();
}
void dfs(int s){
    S.push(s);
    peStiva[s]=1;
    ids[s]=low[s]=id++;

    int nv,i;

    for(i=0;i<ve[s].size();i++){
        nv=ve[s][i];
        if(ids[nv]==0){
            dfs(nv);
            low[s]=min(low[s],low[nv]);
        }
        else if(peStiva[nv]==1)
            low[s]=min(low[s],low[nv]);
    }
    if(ids[s]==low[s]){
        int no;
        ctc++;
        do{
            no=S.top();
            S.pop();
            peStiva[no]=0;
            ct[ctc].push_back(no);
        }while(no!=s);
    }
}
void rezolvare(){
    int i,j;
    for(i=1;i<=n;i++)
        if(ids[i]==0) dfs(i);
    ofstream o("ctc.out");
    o<<ctc<<endl;
    for(i=1;i<=ctc;i++){
        for(j=0;j<ct[i].size();j++){
            o<<ct[i][j]<<" ";
        }
        o<<endl;
    }
    o.close();
}