#include <bits/stdc++.h>

int c, N, M;
std::vector <std::vector <int>> graph;
inline void addEdge(int u, int v) {
    graph[u].push_back(v);
}

class SCCCalculator {
public:
    SCCCalculator (std::vector <std::vector <int>> &graph) { calculate(graph); }
    void calculate(std::vector <std::vector <int>> &graph) {
        _time = 0;
        N = graph.size();
        low    .resize(graph.size(), 0);
        disc   .resize(graph.size(), 0);
        inStack.resize(graph.size(), false);
        for (int i=0; i<graph.size(); ++i)
            if (!disc[i]) DFS(graph, i);
    }

    int getSize() { return components.size(); }
    std::vector <std::vector <int>> getComponents() { return components; }

    std::vector <std::vector <int>> getSCCGraph(std::vector <std::vector <int>>& graph) {
        std::vector <std::vector <int>> SCCGraph;
        SCCGraph.resize(components.size());
        std::vector <bool> seen(components.size(), false);
        for (int i=0; i<components.size(); ++i) {
            for (auto &u:components[i]) {
                for (auto &it:graph[u])
                    if (comp[it] != i && !seen[comp[it]])
                        SCCGraph[i].push_back(comp[it]), seen[comp[it]] = true;
            }
            for (auto &it:SCCGraph[i]) seen[it] = false;
        }   return SCCGraph;
    }

private:
    void DFS(std::vector <std::vector <int>> &graph, int vertex) {
        disc[vertex] = low[vertex] = ++_time;
        inStack[vertex] = true;
        stack.push(vertex);
        for (auto &it:graph[vertex]) {
            if (!disc[it]) { DFS(graph, it);
                low[vertex] = std::min(low[vertex], low[it]);
            }   else
            if (inStack[it]) low[vertex] = std::min(low[vertex], low[it]);
        }
        if (low[vertex] == disc[vertex]) addComponent(vertex);
    }

    void addComponent(int vertex)   {
        components.push_back(std::vector <int>());
        while (!stack.empty() && stack.top() != vertex) {
            components.back().push_back(stack.top());
            inStack[stack.top()] = false;
            stack.pop();
        }   components.back().push_back(stack.top());
            inStack[stack.top()] = false;
            stack.pop();
    }

    int _time;
    int N;
    std::vector <int> low, disc, comp;
    std::vector <std::vector <int>> components;
    std::vector <bool> inStack;
    std::stack  <int> stack;
};

std::ifstream input ("ctc.in");
std::ofstream output("ctc.out");

int main()
{
    input >> N >> M;
    graph.resize(N, std::vector <int>());
    for (int i=0, u, v; i<M; ++i) input >> u >> v, addEdge(u-1, v-1);

    SCCCalculator calc(graph);
    output << calc.getSize() << '\n';
    for (auto &it:calc.getComponents()) {
        for (auto &it2:it) output << it2+1 << ' ';
        output << '\n';
    }

    return 0;
}