#include <fstream>
#include <vector>

using namespace std;

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

int n, m, i, K, x, y, j;
vector <int> ls[100005], lsR[100005];
vector <int> sol[100005];
short viz[100005], care[100005], nc;

void df_inainte(int x) {
    int i;
    viz[x] = 1;
    for (i = 0; i < ls[x].size(); i++)
        if (viz[ ls[x][i] ] == 0)
            df_inainte( ls[x][i] );
    care[++nc] = x;
}

void df_inapoi(int x) {
    int i;
    viz[x] = -1;
    sol[K].push_back(x);
    for (i = 0; i < lsR[x].size(); i++)
        if (viz[ lsR[x][i] ] == 1)
            df_inapoi( lsR[x][i] );
}

int main() {
    f >> n >> m;
    while (m) {
        f >> x >> y;
        ls[x].push_back(y);
        lsR[y].push_back(x);
        m--;
    }

    for (i = 1; i <= n; i++)
        if (viz[i] == 0)
            df_inainte(i);

    for (i = n; i >= 1; i--)
        if (viz[care[i]] != -1) {
            K++;
            df_inapoi(care[i]);
        }
    g << K << '\n';
    for (i = 1; i <= K; i++) {
        for (j = 0; j < sol[i].size(); j++)
            g << sol[i][j] << ' ';
        g << '\n';
    }
    return 0;
}