#include <iostream>
#include <fstream>
#include <stack>
#include <vector>
#include <bitset>

using namespace std;

const int N = 1e5 + 1;

vector <int> L[N], T[N];
vector <vector<int>> scc;
bitset <N> vis;
stack<int> found;
int n;

void Read()
{
    ifstream fin ("ctc.in");
    int m, x , y;
    fin >> n >> m;
    while (m--)
    {
        fin >> x >> y;
        L[x].push_back(y);
        T[y].push_back(x);
    }
    fin.close();
}

void First_DFS(int vertex)
{
    vis[vertex] = 1;
    for (auto& next : L[vertex])
        if (!vis[next])
            First_DFS(next);
    found.push(vertex);
}

void Second_DFS(int vertex)
{
    vis[vertex] = 0;
    scc[scc.size() - 1].push_back(vertex);
    for (auto& next : T[vertex])
        if (vis[next])
            Second_DFS(next);
}

void Kosaraju()
{
    for (int i = 1; i <= n; i++)
        if(!vis[i])
            First_DFS(i);
    while (!found.empty())
    {
        int vertex = found.top();
        found.pop();
        cout << vertex << " ";
        if (vis[vertex])
        {
            scc.push_back({});
            Second_DFS(vertex);
        }
    }
}

void Write()
{
    ofstream fout ("ctc.out");
    fout << scc.size() << "\n";
    for (int i = 0; i < scc.size(); i++, fout << "\n")
        for (int j = 0; j < scc[i].size(); j++)
            fout << scc[i][j] << " ";
    fout.close();

}

int main(){
    Read();
    Kosaraju();
    Write();
    return 0;
}