#include <iostream>
#include <vector>
#include <stack>
#include <fstream>
#include <algorithm>
using namespace std;
void dfs(vector<vector<int>>& edges, stack<int>& result, vector<int>& visited, int start = 1, int time = 1) {
    visited[start] = time;
    for (auto elem : edges[start]) {
        if (visited[elem] == 0) {
            dfs(edges, result, visited, elem, time);
        }
    }
    result.push(start);
}
void reverseDFS_result(stack<int>& result, vector<int>& visited, vector<vector<int>>& edges) {
    for (int i = 0; i < visited.size(); i++) {
        if (visited[i] == 0) {
            dfs(edges, result, visited, i);
        }
    }
}
void strongComponents(stack<int>& result, vector<vector<int>>& edges) {
    int n = result.size();
    int time = 1, visit;
    vector<int> visited(n, 0);
    for (int i = 0; i < n; i++) {
        stack<int> s;
        visit = result.top();
        result.pop();
        if (visited[visit] == 0) {
            dfs(edges, s, visited, visit, time);
        }
        if (!s.empty()) {
            time++;
        }
    }
    vector<vector<int>> strongComponents(time);
    for (int i = 1; i < visited.size(); i++) {
        strongComponents[visited[i]].push_back(i);
    }
    cout << time - 2 << "\n";
    for (int i = 1; i < time; i++) {
        for (auto elem : strongComponents[i]) {
            cout << elem << " ";
        }
        cout << "\n";
    }
    return;
}
int main()
{
    ios_base::sync_with_stdio(false);
    int n, m, s, x, y;
    ifstream in("dfs.in");
    ofstream out("dfs.out");
    in >> n >> m;
    vector<vector<int>> rEdges(n + 1);
    vector<vector<int>> edges(n + 1);
    for (int i = 0; i < m; i++) {
        in >> x >> y;
        edges[x].push_back(y);
        rEdges[y].push_back(x);
    }
    stack<int> result;
    vector<int> visited(n + 1, 0);
    reverseDFS_result(result, visited, rEdges);
    /*while (!result.empty()) {
        cout << result.top() << " ";
        result.pop();
    }*/
    strongComponents(result, edges);
    in.close();
    out.close();
    return 0;
}