#include <bits/stdc++.h>
using namespace std;
ifstream fin("ctc.in");
ofstream fout("ctc.out");
int n, m, sol, nr[100005];
bool used[100005], viz[100005];
vector <int> g[100005], g2[100005], rez[100005];

void dfs(int nod, int var) {
    viz[nod] = true;
    ++nr[nod];
    if (var == 0) {
        for (int i = 0; i < g[nod].size(); ++i) {
            int next = g[nod][i];
            if (!viz[next])
                dfs(next, var);
        }
        return;
    }
    for (int i = 0; i < g2[nod].size(); ++i) {
        int next = g2[nod][i];
        if (!viz[next])
            dfs(next, var);
    }
    return;
}

int main() {
    fin >> n >> m;
    while (m--) {
        int a, b;
        fin >> a >> b;
        g[a].push_back(b);
        g2[b].push_back(a);
    }
    for (int i = 1; i <= n; ++i) {
        if (!used[i]) {
            memset(nr, 0, sizeof nr);
            memset(viz, 0, sizeof viz);
            dfs(i, 0);
            memset(viz, 0, sizeof viz);
            dfs(i, 1);
            ++sol;
            for (int j = 1; j <= n; ++j) {
                if (!used[j] && nr[j] == 2) {
                    used[j] = true;
                    rez[sol].push_back(j);
                }
            }
        }
    }
    fout << sol << "\n";
    for (int i = 1; i <= sol; ++i) {
        for (int j = 0; j < rez[i].size(); ++j)
            fout << rez[i][j] << " ";
        fout << "\n";
    }
    return 0;
}