#include <bits/stdc++.h>
#define Nmax 100005
using namespace std;

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

int N, M, ans;
vector<int> G[Nmax], GT[Nmax], nodes, ctc[Nmax];
bool vis[Nmax];

void DFS1(int node) {
   vis[node] = 1;
   for (auto it: G[node])
      if (!vis[it]) DFS1(it);
   nodes.push_back(node);
}
void DFS2(int node) {
   vis[node] = 1;
   ctc[ans].push_back(node);
   for (auto it: GT[node])
      if (!vis[it]) DFS2(it);
}
int main()
{
    f >> N >> M;
    for (int i = 1; i <= M; ++i) {
        int x, y;
        f >> x >> y;
        G[x].push_back(y);
        GT[y].push_back(x);
    }

    for (int i = 1; i <= N; ++i)
        if (!vis[i]) DFS1(i);
    reverse(nodes.begin(), nodes.end());
    memset(vis, 0, sizeof(vis));

    for (auto it : nodes)
      if (!vis[it]) ++ans, DFS2(it);

    g << ans << '\n';
    for (int i = 1; i <= ans; ++i) {
        for (auto it : ctc[i])
            g << it << " ";
        g << '\n';
    }

    return 0;
}