#include <iostream>
#include <fstream>
#include <vector>
using namespace std;
ifstream f("ctc.in");
ofstream g("ctc.out");
 vector <int> v[100005],vt[100005],sol[100005];
 int n,m,use[100005],k,top[100005],add[100005],ncomp;

 void DF1(int x)
 { int i;
    use[x]=1;

    for(i=0;i<v[x].size();i++)
     if (!use[v[x][i]]) DF1(v[x][i]);

   k++; top[k]=x;
 }

 void DF2(int x)
 { int i;
   add[x]=1;

    for(i=0;i<vt[x].size();i++)
     if (!add[vt[x][i]]) DF2(vt[x][i]);

   sol[ncomp].push_back(x);
 }
int main()
{ int i,x,y,j;
    f>>n>>m;

    for(i=1;i<=m;i++)
     { f>>x>>y;
        v[x].push_back(y);
        vt[y].push_back(x);
     }

     for(i=1;i<=n;i++)
      if (!use[i]) DF1(i);


     for(i=n;i>=1;i--)
      if (!add[top[i]]) {ncomp++; DF2(top[i]);}

       g<<ncomp<<"\n";
      for(i=1;i<=ncomp;i++)
       {for(j=0;j<sol[i].size();j++)
        g<<sol[i][j]<<" ";
          g<<"\n";
       }
    return 0;
}