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

using namespace std;

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

const int N_MAX = 100001;

int n, m, scc;
bool visited[N_MAX];

vector <int> G1[N_MAX], G2[N_MAX], SCC[N_MAX];
stack <int> S;

void Read()
{
    f >> n >> m;
    for (int i = 1; i <= m; i++)
    {
        int x, y;
        f >> x >> y;
        G1[x].push_back(y);
        G2[y].push_back(x);
    }
}

void DFS1(int start)
{
    visited[start] = true;
    for (unsigned int i = 0; i < G1[start].size(); i++)
    {
        int neighbour = G1[start][i];
        if (visited[neighbour] == false)
        {
            DFS1(neighbour);
        }
    }
    S.push(start);
}

void DFS2(int start)
{
    SCC[scc].push_back(start);
    visited[start] = false;
    for (unsigned int i = 0; i < G2[start].size(); i++)
    {
        int neighbour = G2[start][i];
        if (visited[neighbour] == true)
        {
            DFS2(neighbour);
        }
    }
}

int main()
{
    Read();

    for (int i = 1; i <= n; i++)
    {
        if (visited[i] == false)
        {
            DFS1(i);
        }
    }

    while (S.empty() == false)
    {
        int node = S.top();
        if (visited[node] == true)
        {
            scc++;
            DFS2(node);
        }
        S.pop();
    }

    g << scc << "\n";
    for (int i = 1; i <= scc; i++)
    {
        for (unsigned int j = 0; j < SCC[i].size(); j++)
        {
            g << SCC[i][j] << " ";
        }
        g << "\n";
    }
}