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

using namespace std;

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

const int NMAX = 1e5;

int n, m, no;

vector < int > g[1 + NMAX];
vector < int > gi[1 + NMAX];
vector < int > ctc[1 + NMAX];

bitset < 1 + NMAX > vis;
stack < int > st;

bool cmp(vector < int > &a, vector < int > &b) {
  return a[0] < b[0];
}

void dfs1(int node) {
  vis[node] = 1;
  for(int i = 0; i < g[node].size(); i++) {
    int to = g[node][i];
    if(vis[to] == 0)
      dfs1(to);
  }
  st.push(node);
}

void dfs2(int node) {
  vis[node] = 1;
  for(int i = 0; i < gi[node].size(); i++) {
    int to = gi[node][i];
    if(vis[to] == 0)
      dfs2(to);
  }
  ctc[no].push_back(node);
}

int main()
{
  in >> n >> m;
  for(int i = 1; i <= m; i++) {
    int x, y;
    in >> x >> y;
    g[x].push_back(y);
    gi[y].push_back(x);
  }

  for(int i = 1; i <= n; i++)
    if(vis[i] == 0)
      dfs1(i);
  vis = 0;

  while(!st.empty()) {
    int node = st.top();
    st.pop();
    if(vis[node] == 0) {
      no++;
      dfs2(node);
    }
  }

  for(int i = 1; i <= no; i++)
    sort(ctc[i].begin(), ctc[i].end());
  sort(ctc + 1, ctc + no + 1, cmp);

  out << no << '\n';
  for(int i = 1; i <= no; i++) {
    for(int j = 0; j < ctc[i].size(); j++)
      out << ctc[i][j] << ' ';
    out << '\n';
  }

  in.close();
  out.close();
  return 0;
}