#include <fstream>
#include <fstream>
#include <vector>
#include <stack>
#include <bitset>

const int mxN = 1e5 + 5;
std::vector<int> edges[mxN];

int timestamp, curr_size_ans;
std::vector<std::vector<int> > ans;
std::bitset<100005> visited;
std::bitset<100005> in_stack;
std::stack<int> visiting;
int found[mxN], low_link[mxN];

void dfs(int curr_node) {
    found[curr_node] = ++timestamp;
    low_link[curr_node] = found[curr_node];
    visited[curr_node] = true;
    visiting.push(curr_node);
    in_stack[curr_node] = true;

    for (auto neigh : edges[curr_node]) {
        if (!visited[neigh]) {
            dfs(neigh);
            low_link[curr_node] = std::min(low_link[curr_node], low_link[neigh]);
        } if (visited[neigh] && in_stack[neigh]) {
            low_link[curr_node] = std::min(low_link[curr_node], low_link[neigh]);
        }
    }

    if (found[curr_node] == low_link[curr_node]) {
        std::vector<int> new_comp;
        int node;
        do {
            node = visiting.top();
            new_comp.push_back(node);
            visiting.pop();
            in_stack[node] = 0;
        } while (node != curr_node);
        ans.push_back(new_comp);
    }
}

int main() {

    std::ifstream fin("ctc.in");
    std::ofstream fout("ctc.out");

    int n, m;
    fin >> n >> m;

    while (m--) {
        int u, v;
        fin >> u >> v;
        edges[u].push_back(v);
    }

    for (int i = 1; i <= n; ++i) {
        if (!visited[i]) {
            dfs(i);
        }
    }

    fout << ans.size() << '\n';
    for (auto i = 0; i < ans.size(); ++i) {
        std::vector<int> curr_comp = ans[i];
        for (auto elem : curr_comp) {
            fout << elem << " ";
        }
        fout << '\n';
    }
    return 0;
}