#include <bits/stdc++.h>

using namespace std;

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

vector <int> M[100005], aux;

vector <vector<int>> sol;

int idx[100005], lowlink[100005], desc;
bool in_stack[100005];

stack <int> st;

void tarjan(int n)
{
    idx[n] = lowlink[n] = ++desc;
    st.push(n);
    in_stack[n] = 1;

    for (auto it : M[n]) {
        if (idx[it] == 0) {
            tarjan(it);
            lowlink[n] = min(lowlink[n], lowlink[it]);
        } else if (in_stack[it])
            lowlink[n] = min(lowlink[n], lowlink[it]);
    }
    if (idx[n] == lowlink[n]) {
        aux.clear();
        int node;
        do {
            aux.push_back(node = st.top());
            in_stack[node] = 0;
            st.pop();
        } while (node != n);
        sol.push_back(aux);
    }
}

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

    for (int i = 1; i <= n; i++)
        if (idx[i] == 0)
            tarjan(i);

    out << sol.size() << '\n';
    for (int i = 0; i < sol.size(); i++) {
        for (int j = 0; j < sol[i].size(); j++)
            out << sol[i][j] << " ";
        out << '\n';
    }
    return 0;
}