#include <iostream>
#include <fstream>
#include <vector>
#include <queue>
using namespace std;
vector <int> v1[100005],v2[100005];
int n,m,viz[100005],a1[100005],a2[100005];
void df( int nod, vector <int> v[], int apar[])
{
    queue <int> q;
    q.push(nod);
    apar[nod]=1;
    int i,curent;
    while (!q.empty())
    {
        nod=q.front();
        q.pop();
        for(i=0;i<v[nod].size();i++)
        {
            curent=v[nod][i];
            if (apar[curent]==0)
            {
                apar[curent]=1;
                q.push(curent);
            }
        }
    }
}
int main()
{
    int i,x,y;
    fstream f,g;
    f.open("ctc.in",ios::in);
    g.open("ctc.out",ios::out);
    f>>n>>m;
    for (i=1;i<=m;i++)
    {
        f>>x>>y;
        v1[x].push_back(y);
        v2[y].push_back(x);
    }
    int nrc=0;
    g<<"                 \n";
    for (i=1;i<=n;i++)
    {
        if (!viz[i])
        {
            df(i,v1,a1);
            df(i,v2,a2);
            int k;
            nrc++;
            for (k=1;k<=n;k++)
            {
                if (a1[k]==a2[k] && a1[k]==1)
                {
                    viz[k]=1;
                    g<<k<<" ";
                }
                a1[k]=a2[k]=0;

            }
            g<<"\n";
        }
    }
    g.clear();
    g.seekg(0,ios::beg);
    g<<nrc;

}