#include <fstream>
#include <vector>
#define nmax 100000
#define mmax 200000
#define inf 0x3f3f3f3f
using namespace std;
ifstream fin("ctc.in");
ofstream fout("ctc.out");
int n,m,disc[nmax+5],low[nmax+5];
vector<int> v[nmax+5],sol;
vector < vector<int> > comp;
bool viz[nmax+5];
int minv(int x, int y)
{
    return x<y?x:y;
}
void dfs(int u, int parent)
{
    disc[u]=low[u]=disc[parent]+1;
    viz[u]=1;
    sol.emplace_back(u);
    for(int i : v[u])
        if(!viz[i])
        {
            dfs(i,u);
            low[u]=minv(low[u],low[i]);
        }
        else
            low[u]=minv(low[u],low[i]);
    if(disc[u]==low[u])
    {
      comp.emplace_back();
      comp.back().emplace_back(u);
      disc[u]=low[u]=inf;
      while(sol.back()!=u)
      {
          comp.back().emplace_back(sol.back());
          disc[sol.back()]=low[sol.back()]=inf;
          sol.pop_back();
      }
      sol.pop_back();
    }
}
int main()
{
    fin>>n>>m;
    int x,y;
    for(int i=1;i<=m;i++)
        fin>>x>>y,v[x].emplace_back(y);
    for(int i=1;i<=n;i++)
        if(!viz[i])
        dfs(i,0);
    fout<<comp.size()<<"\n";
    for(auto &i:comp)
    {
        for(int j:i)
            fout<<j<<" ";
        fout<<"\n";
    }
    return 0;
}