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

using namespace std;

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

int n, m, scc;
bool visited[100001];
vector <int> V1[100001], V2[100001], vec[100001];
stack <int> S;

void DFS1(int at)
{
    visited[at] = true;
    for (int i = 0; i < V1[at].size(); i++)
    {
        int to = V1[at][i];
        if (visited[to] == false)
        {
            DFS1(to);
        }
    }
    S.push(at);
}

void DFS2(int at)
{
    visited[at] = false;
    vec[scc].push_back(at);
    for (int i = 0; i < V2[at].size(); i++)
    {
        int to = V2[at][i];
        if (visited[to] == true)
        {
            DFS2(to);
        }
    }
}

int main()
{
    f >> n >> m;
    for (int i = 1; i <= m; i++)
    {
        int x, y;
        f >> x >> y;
        V1[x].push_back(y);
        V2[y].push_back(x);
    }

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

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

    g << scc << endl;
    for (int i = 1; i <= scc; i++)
    {
        for (int j = 0; j < vec[i].size(); j++)
        {
            g << vec[i][j] << " ";
        }
        g << endl;
    }
}