#include <fstream>
#include <vector>
#include <cstring>

using namespace std;

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

vector<int> G[100001];
vector<int> T[100001];
vector<int> sol[100001];
int viz[100001];
int vizT[100001];
int vizG[100001];
int comp,n,m;

void DFG(int nod)
{
    if(!vizG[nod])
    {
        vizG[nod] = true;
        for(vector<int>::iterator it = G[nod].begin(); it != G[nod].end(); ++it)
            DFG(*it);
    }
}

void DFT(int nod)
{
    if(!vizT[nod])
    {
        vizT[nod] = true;
        for(vector<int>::iterator it = T[nod].begin(); it != T[nod].end(); ++it)
            DFT(*it);
    }
}

void intersect()
{
    bool flag = false;

    for(int i = 1; i <= m; ++i)
        if(vizG[i] == true && vizT[i] == true)
        {
            flag = true;
            viz[i] = true;

            sol[comp].push_back(i);
        }

    if(flag) comp++;
}

int main()
{
    int x,y;

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

    for(int i = 1; i <= n; ++i)
    {
        if(!viz[i])
        {
            DFG(i);
            DFT(i);
            intersect();
            memset(vizG,false,100001);
            memset(vizT,false,100001);
        }
    }

    g << comp << "\n";
    for(int i = 0; i < comp; ++i)
    {
        for(vector<int>::iterator it = sol[i].begin(); it != sol[i].end(); ++it)
            g << *it << " ";
        g << "\n";
    }

    return 0;
}