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

using namespace std;

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

int const NMAX = 1e5;
int n, m;
vector<int> g[1 + NMAX];
vector<int> scc[1 + NMAX];

int nComp;
stack<int> st;
int time1[1 + NMAX]; //blue label, the time at which we first landed on the node
int lowLink[1 + NMAX]; //red label, the lowest time of a node we could reach from i
int t = 0;
bool onStack[1 + NMAX];

void tarjan(int from) {
  t++;
  time1[from] = t;
  lowLink[from] = t;
  st.push(from);
  onStack[from] = true;
  for(int to : g[from]) {
    if(time1[to] == 0) {
      tarjan(to);
      lowLink[from] = min(lowLink[from], lowLink[to]);
    } else if(onStack[to]) {
      lowLink[from] = min(lowLink[from], lowLink[to]);
    }
  }
  if(lowLink[from] == time1[from]) {
    //cout << "1\n";
    while(!st.empty() && lowLink[from] <= lowLink[st.top()]) {
      scc[nComp].push_back(st.top());
      st.pop();
    }
    //cout << "2\n";
    nComp++;
  }
}

int main(){
  in >> n >> m;
  for(int i = 1; i <= m; i++) {
    int a, b;
    in >> a >> b;
    g[a].push_back(b);
  }
  for(int i = 1; i <= n; i++) {
    if(time1[i] == 0) {
      tarjan(i);
    }
  }
  out << nComp << "\n";
  for(int i = 0; i < nComp; i++) {
    for(int j = 0; j < scc[i].size(); j++) {
      out << scc[i][j] << " ";
    }
    out << "\n";
  }
}