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

using namespace std;

class Graph{
    int n, m;
    std::vector<std::vector<std::pair<int, int>>> graph;
    std::vector<std::vector<int>> ctc;
    std::vector<int> father;
    std::vector<int> distance;
    std::vector<int> lowlink;
    std::vector<int> id;
    std::vector<bool> visited;
    std::stack<int> s;

    int totalCost;
    int index;

    void dfs(const int k){
        visited[k] = true;
        for (const int node : getNeighbors(k)){
            if ( !visited[node] ){
                father[node] = k;
                dfs(node);
            }
        }
        s.push(k);
    }

    void bfs(const int start){
        std::queue<int> q;
        q.push(start);
        visited[start] = true;
        distance[start] = 0;
        while (!q.empty()){
            int node = q.front();
            q.pop();
            for (int neighbor : getNeighbors(node)){
                if (!visited[neighbor]){
                    visited[neighbor] = true;
                    distance[neighbor] = distance[node] + 1;
                    father[neighbor] = node;
                    q.push(neighbor);
                }
            }
        }
    }

    struct edge{
        int cost, x, y;
        bool operator<(const edge o) const{
            return ((this->cost) > o.cost);
        }
    };

    void dijkstra(const int start){
        distance.assign(n+1, 0x7fffffff);
        std::queue<std::pair<int, int>> q;
        q.push({0, start});
        distance[start] = 0;
        while (!q.empty()){
            int currentNode = q.front().second;
            q.pop();
            for (const auto &node : getNeighborsWithWeight(currentNode)){
                if(distance[currentNode] + node.second < distance[node.first])
                {
                    distance[node.first] = distance[currentNode] + node.second;
                    q.push({-distance[node.first], node.first});
                }
            }
        }
    }

    void tarjan(int k){
        visited[k] = true;
        lowlink[k] = id[k] = index++;              //  id-ul reprezinta la al catelea nod in parcurgere am ajuns
        s.push(k);                          //  adaug pe stiva nodul la care sunt
        for (const int x : getNeighbors(k)){            //  parcurg vecinii lui k
            if( !id[x] )                          //  daca id-ul este 0, atunci nodul este nevizitat
                tarjan(x), lowlink[k] = min(lowlink[k], lowlink[x]);  //  DFS + minimul dintre nodul curent(k) si vecinul sau(x) cand vine vorba de label
            else if( visited[x] )                 //  daca nodul vecin(x) este vizitat si se afla pe stiva, atunci nodul curent ia valoarea minima dintre label-ul curent si label-ul vecinului sau(x)
                lowlink[k] = min(lowlink[k], id[x]);
        }
        if(id[k] == lowlink[k]){                    //  daca label-ul (id-ul cel mai mic din componenta conexa) corespunde id-ului, atunci am descoperit componenta tare conexa
            std::vector<int> tmp;
            while(s.top() != k)                 //  golesc toate elementele asociate CTC-ului din stiva
                visited[s.top()] = false, tmp.push_back(s.top()) , s.pop();
            visited[s.top()] = false, tmp.push_back(s.top()), s.pop();      //  construiesc un vector temporar care contine nodurile din CTC
            ctc.push_back(tmp);                 //  Adaug vectorul obtinut la solutie
            tmp.clear();
        }
    }

public:
    explicit Graph(const int n = 0){
        this -> n = n;
        index = totalCost = m = 0;
        graph.resize(n+1);
        father.resize(n+1);
        distance.resize(n+1);
        visited.resize(n+1);
        lowlink.resize(n+1);
        id.resize(n+1);
        ctc.clear();
    }
    void addEdge(const int x, const int y, const int cost = 1){
        graph[x].push_back({y, cost});
        ++m;
    }
    int getEdgeWeight(const int x, const int y) const {
        for (const auto& neighbor : graph[x]) {
            if (neighbor.first == y) {
                return neighbor.second;
            }
        }
        return (int)0x80000000;
    }

    std::vector<int> getNeighbors(const int x) const {
        std::vector<int> neighbors;
        for (const auto& neighbor : graph[x]) {
            neighbors.push_back(neighbor.first);
        }
        return neighbors;
    }

    std::vector<std::pair<int, int>> getNeighborsWithWeight(const int x) const {
        return graph[x];
    }

    std::stack<int> topologicalSort() {
        visited.assign(n+1, false);
        for (int i = 1; i <= n; ++i) {
            if (!visited[i]) {
                dfs(i);
            }
        }
        return s;
    }

    void removeEdge(const int x, const int y){
        for (auto it = graph[x].begin(); it != graph[x].end(); ++it) {
            if (it -> first == y) {
                graph[x].erase(it);
                --m;
                return;
            }
        }
    }

    void removeNode(const int x){
        for (int i = 1; i <= n; ++i) {
            removeEdge(i, x);
            removeEdge(x, i);
        }
        graph[x].clear();
        --n;
    }

    std::vector<std::pair<int, int>> MST(int x){
        std::vector<std::pair<int, int>> mst;
        visited.assign(n+1, false);
        visited[x] = true;
        std::priority_queue<edge> q;
        for(auto e : getNeighborsWithWeight(x)) {
            edge V{e.second, x, e.first};
            q.push(V);
        }
        while (!q.empty()){
            edge k = q.top();
            q.pop();
            if(visited[k.y] == 0) {
                mst.push_back({k.x, k.y});
                totalCost += k.cost;
                visited[k.y] = true;
                for (auto e: graph[k.y]) {
                    edge V{e.second, k.y, e.first};
                    q.push(V);
                }
            }
        }
        return mst;
    }

    int getCost() const {
        return totalCost;
    }

    int getShortestPathFromTo(const int from, const int to){
        dijkstra(from);
        return distance[to];
    }

    std::vector<int> getDistancesFrom(const int from){
        dijkstra(from);
        return distance;
    }

    int howManyCC(){
        int count = 0;
        visited.assign(n+1, false);
        for (int i = 1; i <= n; ++i)
            if(!visited[i]) {
                dfs(i);
                ++count;
            }
        return count;
    }

    std::vector<std::vector<int>> CTC(){
        lowlink.resize(n+1, 0);
        id.resize(n+1, 0);
        index = 1;
        ctc.clear();
        for (int i = 1; i <= n; ++i) {
            if( !id[i] )
                tarjan(i);
        }
        return ctc;
    }
};

int main() {
    ifstream in("ctc.in");
    int n, m;
    in >> n >> m;
    Graph g(n);
    while (m--){
        int x, y;
        in >> x >> y;
        g.addEdge(x, y);
    }
    in.close();
    ofstream out("ctc.out");
    auto sol = g.CTC();
    out << sol.size() << '\n';
    for (auto x : sol) {
        sort(x.begin(), x.end());       //  sortez pentru ca nodurile din CTC sa fie prezentate in ordine crescatoare
        for (auto y: x) {
            out << y << ' ';
        }
        out << '\n';
    }
    out.close();
    return 0;
}