#include <fstream>
#include <vector>
#include <bitset>
#include <map>
#define Nmax 100009

using namespace std;
ifstream f("ctc.in");
ofstream g("ctc.out");

int n,m,x,y,nrsol;
vector <int> G[Nmax],Gt[Nmax],sol[Nmax];
bitset <Nmax> viz1,viz2,v1,v2,used;
map <int,int> ctc;

void ReadInput()
{
    f>>n>>m;
    for (int i=1; i<=m; ++i)
    {
        f>>x>>y;
        G[x].push_back(y);
        Gt[y].push_back(x);
    }
}

void Dfs(int node, map <int,int>& v, vector<int> G[Nmax],bitset <Nmax>& viz)
{
    viz[node]=1;
    ++v[node];
    for (auto x : G[node])
        if (!viz[x])
        if (!used[x]) Dfs(x,v,G,viz);
}

void Solve()
{
    for (int i=1; i<=n; ++i)
        if (!used[i])
        {
            ctc.clear();
            Dfs(i,ctc,G,viz1);
            Dfs(i,ctc,Gt,viz2);
            ++nrsol;
            for (auto x: ctc)
            if (x.second==2)
            {
                used[x.first]=1;
                sol[nrsol].push_back(x.first);
            }
            viz1.reset();
            viz2.reset();
        }
}

void Write()
{
    g<<nrsol<<'\n';
    for (int i=1; i<=nrsol; ++i)
    {
        for (auto x: sol[i]) g<<x<<' ';
        g<<'\n';
    }
}

int main()
{
    ReadInput();
    Solve();
    Write();
    f.close();
    g.close();
    return 0;
}