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

using namespace std;

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

const int MAX = 100005;

vector < int > G[MAX], GT[MAX], Rezultate[MAX];
stack < int > ST;

int n, m, viz[MAX], nr_ctc;

void dfs(int nod) {
    viz[nod] = 1;
    for (unsigned int i = 0; i < G[nod].size(); i++)
        if (!viz[G[nod][i]])
            dfs(G[nod][i]);
    ST.push(nod);
}

void dfs_t(int nod) {
    viz[nod] = 2;
    Rezultate[nr_ctc].push_back(nod);
    for (unsigned int i = 0; i < GT[nod].size(); i++)
        if (viz[GT[nod][i]] == 1)
            dfs_t(GT[nod][i]);
}

int main() {

    in >> n >> m;

    for (int i = 1; i <= m; i++) {
        int x, y;
        in >> x >> y;
        G[x].push_back(y);
        GT[y].push_back(x);
    }

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

    while (!ST.empty()) {
        int nod = ST.top();
        ST.pop();
        if (viz[nod] == 1) {
            nr_ctc++;
            dfs_t(nod);
        }
    }

    out << nr_ctc << '\n';
    for (int i = 1; i <= nr_ctc; i++) {
        for (unsigned int j = 0; j < Rezultate[i].size(); j++)
            out << Rezultate[i][j] << ' ';
        out << '\n';
    }

    return 0;
}