#include <fstream>
#include <vector>
using namespace std;
const int NMAX = 100001;
int N, M, nrc;
vector <int> G[NMAX], GT[NMAX], CTC[NMAX], Post;
bool viz[NMAX];
ifstream f("ctc.in");
ofstream g("ctc.out");
void citire()
{
    int x, y;
    f >> N >> M;
    while(M--)
    {
        f >> x >> y;
        G[x].push_back(y);
        GT[y].push_back(x);
    }
}
void dfs(int vf)
{
    viz[vf] = 1; ///+
    for(const auto &x : G[vf])
        if(viz[x] == 0)
            dfs(x);
    Post.push_back(vf);
}
void dfsGT(int vf)
{
    viz[vf] = 0;
    CTC[nrc].push_back(vf);
    for(const auto &x : GT[vf])
        if(viz[x] == 1)
            dfsGT(x);
}
void componente()
{
    for(int i = 1; i <= N; i++)
        if(viz[i] == 0)
            dfs(i);
    for(auto it = Post.rbegin(); it != Post.rend(); it++)
        if(viz[*it] == 1)
        {
            nrc++;
            dfsGT(*it);
        }
}
void afisare()
{
    g << nrc << '\n';
    for(int i = 1; i <= nrc; i++)
    {
        for(const auto &x : CTC[i])
            g << x << ' ';
        g << '\n';
    }
}
int main()
{
    citire();
    componente();
    afisare();
    f.close();
    g.close();
    return 0;
}