#include <bits/stdc++.h>
#define ll long long
using namespace std;

void dfs(int v, const vector<vector<int>>& adj, vector<int>& vis, vector<int>& st) {
    vis[v] = -1;
    for (auto u : adj[v]) {
        if (!vis[u]) {
            dfs(u, adj, vis, st);
        }
    }
    st.push_back(v);
}

void dfs2(int v, int root, const vector<vector<int>>& inv, vector<int>& vis) {
    vis[v] = root;
    for (auto u : inv[v]) {
        if (vis[u] == -1) {
            dfs2(u, root, inv, vis);
        }
    }
}

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

void solve() {
    int n, m;
    fin >> n >> m;
    vector<int> st;
    vector<vector<int>> adj(n, vector<int>()), inv(n, vector<int>());
    while (m--) {
        int x, y;
        fin >> x >> y;
        x--;
        y--;
        adj[x].push_back(y);
        inv[y].push_back(x);
    }
    vector<int> vis(n, 0);
    for (int i = 0; i < n; i++) {
        if (!vis[i]) {
            dfs(i, adj, vis, st);
        }
    }
    int ans = 0;
    vector<vector<int>> comp(n, vector<int>());
    for (int i = n - 1; i >= 0; i--) {
        if (vis[st[i]] == -1) {
            ans++;
            dfs2(st[i], ans, inv, vis);
        }
    }
    fout << ans << endl;
    for (int i = 0; i < n; i++) {
        comp[vis[i]].push_back(i + 1);
    }
    for (int i = 1; i < ans + 1; i++) {
        for (int j = 0; j < comp[i].size(); j++) {
            fout << comp[i][j] << " ";
        }
        fout << endl;
    }
}

int main() {
    int t = 1;
    while (t--) {
        solve();
    }
}