#include <iostream>
#include <algorithm>
#include <fstream>
#include <vector>
#include <list>
#include <stack>

using namespace std;

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

class Graph {
    int vertices;
    list <int> *adj;

    vector <vector <int>> ans;

public:
    Graph(int v) : vertices(v) {
        adj = new list <int>[v];
    }

    void addEdge(int from, int to) {
        adj[from].push_back(to);
    }

    void depthFirst(int i, vector <int> &disc, vector <int> &low, stack <int> &st, vector <bool> &stackMember) {
        static int id = 0;

        disc[i] = low[i] = ++id;
        st.push(i);
        stackMember[i] = true;

        for (auto &adjVal : adj[i]) {
            if (!disc[adjVal]) {
                depthFirst(adjVal, disc, low, st, stackMember);

                low[i] = min(low[i], low[adjVal]);
            }

            else
                if (stackMember[adjVal])
                    low[i] = min(low[i], disc[adjVal]);
        }

        if (low[i] == disc[i]) {
            vector <int> newAns;

            while (st.top() != i) {
                int topVal = st.top();
                st.pop();
                stackMember[topVal] = false;
                newAns.push_back(topVal);
            }

            int topVal = st.top();
            st.pop();
            stackMember[topVal] = false;
            newAns.push_back(topVal);

            ans.push_back(newAns);
        }
    }

    void findSCC() {
        vector <int> disc(vertices), low(vertices);
        vector <bool> stackMember(vertices);
        stack <int> st;

        for (int i = 1; i <= vertices; ++i) {
            if (!disc[i])
                depthFirst(i, disc, low, st, stackMember);
        }
    }

    void printData() {
        out << ans.size() << "\n";
        
        for (size_t j = 0; j < ans.size(); ++j) {
            sort(ans[j].begin(), ans[j].end());
            for (size_t i = 0; i < ans[j].size(); ++i) {
                out << ans[j][i];
                if (i + 1 != ans[j].size())
                    out << " ";
            }
            if (j + 1 != ans.size())
                out << "\n";
        }
    }

};

int main() {

    int N, M;

    in >> N >> M;

    Graph *myGraph = new Graph(N + 1);

    while (M--) {
        int from, to;
        in >> from >> to;
        myGraph -> addEdge(from, to);
    }

    myGraph -> findSCC();

    myGraph -> printData();

    in.close();
    out.close();
    return 0;
}