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

using namespace std;

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

int const NMAX = 1e5;

struct Node {
  int visited;  //at which step did we visit the node
  int minReach; //the node with the minimum visited that I can reach
  bool onStack;
};

int n, m;
int strongSiz;

Node v[1 + NMAX];
vector <int> g[1 + NMAX];
vector <int> strong[1 + NMAX];
stack<int> st;

int step = 0;

void computeStrong(int from) {
  step++;
  v[from].visited = step;
  v[from].minReach = from; //cand updates minReach ma uit la visited
  st.push(from);
  v[from].onStack = true;
  for(int i = 0; i < g[from].size(); i++) {
    int to = g[from][i];
    if(v[to].visited == 0){
      computeStrong(to);
      if(v[v[from].minReach].visited > v[v[to].minReach].visited) {
        v[from].minReach = v[to].minReach;
      }
    } else if(v[to].onStack == true) {
      if(v[v[from].minReach].visited > v[to].visited) {
        v[from].minReach = to;
      }
    }
  }
  if(v[from].minReach == from) {
    strongSiz++;
    int popped;
    do {
      popped = st.top();
      st.pop();
      strong[strongSiz].push_back(popped);
      v[popped].onStack = false;
    } while (popped != from);
  }
}

int main() {

  int a, b;
  in >> n >> m;
  for(int i = 1; i <= m; i++) {
    in >> a >> b;
    g[a].push_back(b);
  }
  for(int i = 1; i <= n; i++) {
    if(v[i].visited == 0) {
      computeStrong(i);
    }
  }
  out << strongSiz << '\n';
  for(int i = 1; i <= strongSiz; i++) {
    for(int j = 0; j < strong[i].size(); j++) {
      out << strong[i][j] << ' ';
    }
    out << '\n';
  }
  return 0;
}