#include <iostream>
#include <fstream>
#include <bitset>
#include <vector>
#define nmax 100000
#define inf 0x3f3f3f3f
using namespace std;
ifstream fin("ctc.in");
ofstream fout("ctc.out");
int n,m,disc[nmax+5],low[nmax+5],timp;
vector<int> g[nmax+5],sol;
vector<vector<int> > comp;
bitset<nmax+5> viz;
int minv(int x,int y)
{
    return x<y?x:y;
}
void dfs(int nod)
{
    disc[nod]=low[nod]=++timp;
    viz[nod]=1;
    sol.push_back(nod);
    int son;
    for(int fiu : g[nod])
    if(!viz[fiu])
    {
        dfs(fiu);
        low[nod]=minv(low[nod],low[fiu]);    }
    else
    low[nod]=minv(low[nod],low[fiu]);
    if(disc[nod]==low[nod])
    {
        comp.emplace_back();
      do
      {
          comp.back().emplace_back(sol.back());
          disc[sol.back()]=low[sol.back()]=inf;
          sol.pop_back();
      }while(*(&(sol.back())+1)!=nod);
    }
}
int main()
{
    fin>>n>>m;
    int x,y;
    for(int i=1;i<=m;i++)
    {
        fin>>x>>y;
        g[x].push_back(y);
    }
    for(int i=1;i<=n;i++)
        if(!viz[i])
        dfs(i);
    fout<<comp.size()<<"\n";
    for(auto &i:comp)
    {
        for(int j:i)
            fout<<j<<" ";
        fout<<"\n";
    }
    return 0;
}