#include<iostream>
#include<fstream>
#include<bitset>
#include<vector>
#include<stack>
using namespace std;
int n,ids[50010],low[50010],id=1,ctc=0;
vector <int> ve[50010];
vector <int> ct[50010];
stack <int> S;
bitset <50010> peStiva;
void dfs(int s){
    peStiva[s]=1;
    S.push(s);
    ids[s]=low[s]=id++;

    int i,nv,no;

    for(i=0;i<ve[s].size();i++){
        nv=ve[s][i];
        if(ids[nv]==0) dfs(nv);
        if(peStiva[nv]) low[s]=min(low[s],low[nv]);
    }
    if(low[s]==ids[s]){
        ctc++;
        do{
            no=S.top();
            //cout<<no<<endl;
            S.pop();
            ct[ctc].push_back(no);
            peStiva[no]=0;
        }while(no!=s);
        cout<<endl;
    }
}
int main(){
    ifstream f("ctc.in");
    int m,i,x,y,j; f>>n>>m;
    for(i=1;i<=m;i++){
        f>>x>>y;
        ve[x].push_back(y);
    }
    f.close();
    for(i=1;i<=n;i++)
        if(ids[i]==0) dfs(i);
    f.close();
    ofstream o("ctc.out");
    o<<ctc<<endl;
    for(i=1;i<=ctc;i++){
        for(j=0;j<ct[ctc].size();j++)
            o<<ct[i][j]<<" ";
        o<<endl;
    }
    o.close();
}