//#include <iostream>
#include <fstream>
#include <list>
#include <vector>
#include <stack>
#define nmax 100999
using namespace std;

list<int> g[nmax];
list<int> com[nmax];
vector<bool> proceded(nmax,false);
int timp,dfn[nmax],t[nmax],n,low[nmax],comp[nmax],nrc;
stack<int > st;

ifstream fin("ctc.in");
ofstream fout("ctc.out");

void afisare(int x)
{int t;nrc++;
    do{
        t=st.top();
        comp[t]=nrc;
        st.pop();
   //  cout<<t<<' ';
    }while(t!=x);
   // cout<<endl;
}

void citire(){
    int m,x,y;
    fin>>n>>m;
    while(m--)
    {
        fin>>x>>y;
        g[x].push_back(y);
    }
}


void dfs(int x)
{
dfn[x]=++timp;
int y;
    for(list<int>::iterator it=g[x].begin(); it!=g[x].end(); it++)
    {y=*it;
     //st.push(y);

     if(!dfn[y])
        {   //Tree edge:
           st.push(y);
            t[y]=x;
            dfs(y);
        }
    else if(dfn[y]<dfn[x] && !proceded[y]){
     //Back-edges:
        if(dfn[y] < dfn[ low[x] ])
            low[x]=y;

    }
    else if(dfn[y]<dfn[x] &&  proceded[y]){
     //Cross-edge:
        if(!comp[y])
            if(dfn[y] < dfn[low[x]])
                low[x]=y;
    }
}

if( low[x] ==x )
        afisare(x);

if( dfn[ low[t[x]] ] > dfn[low[x]])
        low[t[x]]=low[x];

proceded[x]=1;
}

int main()
{
    citire();
    int i;
    for(i=1;i<=n;i++)low[i]=i;
    for(i=1;i<=n;i++)
        {st.push(i);
        if(!dfn[i])dfs(i);}

    for(i=1;i<=n;i++)
        com[comp[i]].push_back(i);
    fout<<nrc<<'\n';
    for(i=1;i<=nrc;i++)
    {for(list<int>::iterator it=com[i].begin();it!=com[i].end();it++)
        fout<<*it<<' ';
    fout<<'\n';}


}