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

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

std::vector<std::vector<int>> adj;
std::vector<std::vector<int>> trans;
std::vector<int> viz;
std::stack<int> sortat;
std::vector<std::vector<int>> sol;

int comp;

void DFS(int nod) {
    viz[nod] = 1;
    for (int i : adj[nod])
        if (!viz[i])
            DFS(i);
    sortat.push(nod);
}

void DFS2(int nod) {
    viz[nod] = 0;
    for (int i : trans[nod])
        if (viz[i])
            DFS2(i);
    sol[comp].push_back(nod);
}

int main() {
    int n,m;
    f >> n >> m;

    adj.resize(n + 1);
    trans.resize(n + 1);
    viz.resize(n + 1);
    sol.resize(n + 1);

    for (int i = 0 ; i < m; i++) {
        int x,y;
        f >> x >> y;
        adj[x].push_back(y);
        trans[y].push_back(x);
    }

    for (int i = 1; i <= n; i++) {
        if (!viz[i])
            DFS(i);
    }

    while (!sortat.empty()) {
        int nod = sortat.top();
        sortat.pop();
        if (viz[nod]) {
            DFS2(nod);
            comp++;
        }
    }

    g << comp << '\n';
    for (int i = 0; i < comp; i ++) {
        for (int j : sol[i])
            g << j << ' ';
        g << '\n';
    }

    return 0;
}