#include <bits/stdc++.h>
#define Nmax 100002
using namespace std;
ifstream fin("ctc.in");
ofstream fout("ctc.out");

vector <int> L[Nmax];
vector <int> T[Nmax];
vector <int> sol[Nmax];
int n,m,viz[Nmax],st[Nmax],k,nc;
void Citire()
{
    int i,x,y;
    fin>>n>>m;
    for(i=1;i<=m;i++)
    {
        fin>>x>>y;
        L[x].push_back(y);
        T[y].push_back(x);
    }
    fin.close();
}

inline void DFS1(int nod)
{
    int i;
    viz[nod]=1;
    for(i=0;i<L[nod].size();i++)
        if(!viz[L[nod][i]])
            DFS1(L[nod][i]);
    st[++k]=nod;
}

inline void DFS2(int nod)
{
    int i;
    viz[nod]=0;
    for(i=0;i<T[nod].size();i++)
        if(viz[T[nod][i]])
            DFS2(T[nod][i]);
    sol[nc].push_back(nod);
}

void Rezolvare()
{
    int i;
    for(i=1;i<=n;i++)
        if(!viz[i])
            DFS1(i);
    while(k)
    {
        i=st[k--];
        if(viz[i])
        {
            nc++;
            DFS2(i);
        }
    }
    int j;
    fout<<nc<<"\n";
    for(i=1;i<=nc;i++)
    {
        for(j=0;j<sol[i].size();j++)
            fout<<sol[i][j]<<" ";
        fout<<"\n";
    }
    fout.close();
}

int main()
{
    Citire();
    Rezolvare();
    return 0;
}