#include <bits/stdc++.h>

using namespace std;

const int kNmax = 1e5+5;

int n, m;
vector<int> g[kNmax];
vector<int> gt[kNmax];
vector<int> cc[kNmax];

vector<int> order;

int cc_of_node[kNmax], used[kNmax];

void dfp(int x) {
  used[x] = 1;
  for (int y : g[x]) {
    if (used[y]) continue;
    dfp(y);
  }
  order.push_back(x);
}

void dfm(int x, int which) {
  if (cc_of_node[x] != 0) return;
  cc_of_node[x] = which;
  for (int y : gt[x]) {
    if (cc_of_node[y] != 0) continue;
    dfm(y, which);
  }
}

int main() {
  #ifdef INFOARENA
  freopen("ctc.in", "r", stdin);
  freopen("ctc.out", "w", stdout);
  #endif
  
  cin >> n >> m;
  for (int x, y, i = 1; i <= m; i++) {
    cin >> x >> y;
    g[x].push_back(y);
    gt[y].push_back(x);
  }
  
  for (int i = 1; i <= n; i++) {
    if (used[i]) continue;
    dfp(i);
  }
  
  int count = 1;
  for (int i = n - 1; i >= 0; --i) {
    if (cc_of_node[order[i]]) continue;
    dfm(order[i], count++);
  }
  --count;
  
  for (int i = 1; i <= n; i++) {
    cc[cc_of_node[i]].push_back(i);
  }
  
  cout << count << '\n';
  for (int i = 1; i <= count; i++) {
    for (int node : cc[i])
      cout << node << ' ';
    cout << '\n';
  }
  
  return 0;
}