//#include <iostream>
#include <fstream>
#include <vector>
#define MA 100005
using namespace std;
ifstream fin("ctc.in");
ofstream fout("ctc.out");
vector <int> a[MA],at[MA],rez[MA];
int va[MA],Ga[MA],Gat[MA],tfa[MA],ctc[MA];
int n,k,nrcompcon;

void DFS(int x)
{
    va[x]=1;
    for(int i=0;i<Ga[x];i++)
        if(!va[ a[x][i]  ])
            DFS(a[x][i]);
    tfa[++k]=x;
    //cout<<x<<' ';
}
void DFSt(int x)
{
    ctc[x]=nrcompcon;
    rez[nrcompcon].push_back(x);
    for(int i=0;i<Gat[x];i++)
        if(!ctc[at[x][i]])
            DFSt(at[x][i]);
}
void Citire()
{
    int x,y,i,m;
    fin>>n>>m;
    for(i=1;i<=m;i++)
    {
        fin>>x>>y;
        a[x].push_back(y);
        at[y].push_back(x);
    }
    for(i=1;i<=n;i++)
        {
            Ga[i]=a[i].size();
            Gat[i]=at[i].size();
        }
}

void Rezolva()
{
    int i,x;
    for(i=1;i<=n;i++)
        if(!va[i])
            DFS(i);
    for(i=n;i>=1;i--)
    {
        x=tfa[i];
        if(ctc[x]==0)
        {
            nrcompcon++;
            DFSt(x);
        }
    }

    fout <<nrcompcon<<'\n';
    for(i=1;i<=nrcompcon;i++)
        if(rez[i].size()>0)
        {
            for(int j=0;j<rez[i].size();j++)
                fout<<rez[i][j]<<' ';
            fout<<'\n';
        }
}

int main()
{
    Citire();
    Rezolva();
    fin.close();
    fout.close();
    return 0;
}