#include <fstream>
#include <vector>
#include <stack>
#include <set>

using namespace std;

int n, m, i, j, k, start, ord[100003], levMin[100003];
vector<int> vec[100003], comp[100003];
stack<int> stiva;
set<int> s;

void func(int nod) {
    int p, x;

    ord[nod] = start;
    levMin[nod] = start;
    start++;
    stiva.push(nod);
    s.insert(nod);

    for(p = 0; p < vec[nod].size(); p++)
        if(!ord[vec[nod][p]]) {   /// vecinii nevizitati
            func(vec[nod][p]);  /// func()
            levMin[nod] = min(levMin[nod], levMin[vec[nod][p]]);   /// actualizez nivelul radacinii
        }
        else if(s.find(vec[nod][p]) != s.end()) /// daca stiva contine vecinul
           levMin[nod] = min(levMin[nod], ord[vec[nod][p]]);   /// actualizez nivelul radacinii

    if(ord[nod] == levMin[nod])
        while(!stiva.empty()) {    /// in componenta conexa intra toate nodurile din stiva, care sunt deasupra lui nod
            x = stiva.top();
            stiva.pop();
            s.erase(x);
            comp[k].push_back(x);
            if(x == nod) {
                k++;
                break;
            }
        }
}

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

    f >> n >> m;
    while(m) {
        f >> i >> j;

        vec[i].push_back(j);
        m--;
    }
    f.close();

    k = 0;
    start = 1;
    for(i = 1; i <= n; i++)
        if(!ord[i])
            func(i);
    g << k << '\n';

    for(i = 0; i < k; i++, g << '\n')
        for(j = 0; j < comp[i].size(); j++)
            g << comp[i][j] << ' ';

    g.close();

    return 0;
}