#include <bits/stdc++.h>

using namespace std;

const int N = (int) 1e5 + 7;
int n, m;
bool vis[N];
vector<int> g[N], ginv[N], ord, now;
vector<vector<int>> ret;

void dfs(int a) {
  vis[a] = 1;
  for (auto &b : g[a]) if (!vis[b]) dfs(b);
  ord.push_back(a);
}

void dfs2(int a) {
  now.push_back(a);
  vis[a] = 1;
  for (auto &b : ginv[a]) if (!vis[b]) dfs2(b);
}

signed main() {
  freopen ("ctc.in", "r", stdin), freopen ("ctc.out", "w", stdout);
  cin >> n >> m;
  for (int i = 1; i <= m; i++) {
    int x, y; cin >> x >> y;
    g[x].push_back(y);
    ginv[y].push_back(x);
  }
  for (int i = 1; i <= n; i++) if (!vis[i]) dfs(i);
  for (int i = 1; i <= n; i++) vis[i] = 0;
  reverse(ord.begin(), ord.end());
  for (auto &x : ord) if (!vis[x]) now.clear(), dfs2(x), ret.push_back(now);
  cout << (int) ret.size() << "\n";
  for (auto &v : ret) {for (auto &x : v) cout << x << " "; cout << "\n";}
}