#include <iostream>
#include <fstream>
#include <vector>
#include <queue>
#include <stack>

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

const int NMAX = 1e5;
std::vector<int> L[NMAX + 1];
std::vector<int> ids, lowlink;
std::vector<bool> onStack;
std::stack<int> st;
int id;
std::vector<std::vector<int>> scc;

void strongConnect(int at) {
    st.push(at);
    onStack[at] = true;
    ids[at] = lowlink[at] = id++;

    for (auto to: L[at]) {
        if (ids[to] == -1) {
            strongConnect(to);
            lowlink[at] = std::min(lowlink[at], lowlink[to]);
        }
        else if (onStack[to]) {
            lowlink[at] = std::min(lowlink[at], lowlink[to]);
        }
    }

    if (ids[at] == lowlink[at]) {
        std::vector<int> component;
        while (true) {
            auto node = st.top();
            st.pop();
            onStack[node] = false;
            component.push_back(node);
            if (node == at) break;
        }
        scc.push_back(component);
    }
}
int viz[NMAX + 1];
int N, M;


int main() {

    f >> N >> M;
    for(int i = 1; i <= M; ++i){
        int x, y;
        f >> x >> y;
        L[x].push_back(y);

    }

    ids.assign(N+1, -1);
    onStack.assign(N+1, false);
    lowlink.assign(N+1, 0);

    for (int i = 1; i <= N; i++) {
        if (ids[i] == -1) {
            strongConnect(i);
        }
    }

    g << scc.size() << "\n";

    for (const auto& component: scc){
        for (auto node: component)
            g << node << " ";
        g << '\n';
    }



    return 0;
}