#include <vector>
#include <fstream>

#define NMAX 100010
using std::vector;

std::ifstream fin("ctc.in");
std::ofstream fout("ctc.out");

int n, m;
vector<int> ad1[NMAX];
vector<int> ad2[NMAX];

bool done[NMAX];
bool plus[NMAX];
bool minus[NMAX];

int nrComp;
vector<int> comp[NMAX];

void dfs(vector<int> ad[], bool vis[], int node) {
    vis[node] = true;
    for (int i = 0; i < (int) ad[node].size(); i++)
        if (!vis[ad[node][i]])
            dfs(ad, vis, ad[node][i]);
}

void start(int src) {
    for (int i = 1; i <= n; i++)
        plus[i] = minus[i] = false;

    dfs(ad1, plus, src);
    dfs(ad2, minus, src);

    for (int i = 1; i <= n; i++)
        if (plus[i] && minus[i]) {
            done[i] = true;
            comp[nrComp].push_back(i);
        }
    nrComp++;
}

int main() {
    fin >> n >> m;
    for (int i = 0; i < m; i++) {
        int x, y;
        fin >> x >> y;

        ad1[x].push_back(y);
        ad2[y].push_back(x);
    }

    for (int i = 1; i <= n; i++)
        if (!done[i])
            start(i);

    fout << nrComp << '\n';
    for (int i = 0; i < nrComp; i++) {
        for (int j = 0; j < (int) comp[i].size(); j++)
            fout << comp[i][j] << ' ';
        fout << '\n';
    }

    fout.close();
    return 0;
}