#include <fstream>
#include <vector>
using namespace std;
ifstream f("ctc.in");
ofstream g("ctc.out");
vector <int> v[100001];
vector <int> v1[100001];
vector <int> v2[100001];
 int n,m,j,sel[100001],of[100001],nr,q,y;
 void df(int x)
 {
     int i;
     sel[x]=1;
     for (i=0;i<v[x].size();i++)
     {
         y=v[x][i];
         if (sel[y]==0)
         {
             df(y);
         }
     }
     of[++nr]=x;
 }
 void df2(int x)
 {
     int i;
     sel[x]=1;
     for (i=0;i<v1[x].size();i++)
     {
         y=v1[x][i];
         if (sel[y]==0)
         {
             df2(y);
         }
     }
     v2[q].push_back(x);
 }
 int x,i;
int main()
{

    f>>n>>m;
    for (i=1;i<=m;i++)
    {
        f>>x>>y;
        v[x].push_back(y);
        v1[y].push_back(x);
    }
    for (i=1;i<=n;i++)
    {
        if (sel[i]==0)
        {
            df(i);
        }
    }
    for (i=1;i<=n;i++)sel[i]=0;
    for (i=nr;i>=1;i--)
    {
        if (sel[of[i]]==0)
        {
            q++;
            df2(of[i]);
        }
    }
    g<<q<<'\n';
    for (i=1;i<=q;i++)
    {
        for (j=0;j<v2[i].size();j++)
        {
            g<<v2[i][j]<<" ";
        }
        g<<'\n';
    }
    return 0;
}