#include <iostream>
#include <vector>
#include <map>
#include <algorithm>
#include <climits>
using namespace std;
#define int long long
constexpr int MAXN = 1e6 + 5;
int cnt, cnm;
int head1[MAXN], head2[MAXN];
bool vis1[MAXN], vis2[MAXN];
vector<int> result[MAXN];
struct Node {
    int next, to;
}e1[100005], e2[100005];
int n, m;
int xb[MAXN];
int num[MAXN];
map<int, int> mp;
map<pair<int, int>, bool> pd;

void init() {
    cnt = 0;
    for (int i = 0; i < MAXN; i++) {
        head2[i] = head1[i] = -1;
    }
}

void add(int x, int y) {
    e1[cnt].to = y;
    e1[cnt].next = head1[x];
    head1[x] = cnt;

    e2[cnt].to = x;
    e2[cnt].next = head2[y];
    head2[y] = cnt++;
}

void DFS1(int k) {
    vis1[k] = 1;
    for (int i = head2[k]; ~i; i = e2[i].next) {
        int v = e2[i].to;
        if (!vis1[v]) {
            DFS1(v);
        }
    }
    num[++cnm] = k;
}

void DFS2(int k, int fa) {
    mp[fa] = min(mp[fa], k);
    vis2[k] = 1;
    xb[k] = fa;
    for (int i = head1[k]; ~i; i = e1[i].next) {
        int v = e1[i].to;
        if (!vis2[v]) {
            DFS2(v, fa);
        }
    }
}

void kosaraju() {
    for (int i = 1; i <= n; i++) {
        if (!vis1[i]) {
            DFS1(i);
        }
    }

    for (int i = n; i >= 1; i--) {
        if (!vis2[num[i]]) {
            mp[num[i]] = INT_MAX;
            DFS2(num[i], num[i]);
        }
    }
}

main() {
    init();
    cin >> n >> m;
    while (m--) {
        int x, y;
        cin >> x >> y;
        if (x == y) continue;
        if (pd[{x, y}]) continue;
        pd[{x, y}] = true;
        add(x, y);
    }

    kosaraju();

    for (int i = 1; i <= n; i++) {
        result[mp[xb[i]]].push_back(i);
    }

    for (auto& [i, j] : mp) {
        sort(result[i].begin(), result[i].end());
    }
    int ssum = 0;
    vector<bool> sf(n + 1, false);
    vector<vector<int>> out;

    for (int i = 1; i <= n; i++) {
        int root = mp[xb[i]];
        if (!sf[root] && !result[root].empty()) {
            ssum++;
            out.push_back(result[root]);
            sf[root] = true;
        }
    }

    cout << ssum << endl;
    vector<bool> vis(n + 1, false);
    for (int i = 1; i <= n; i++) {
        if (!vis[i]) {
            int root = xb[i];
            for (int node : result[root]) {
                cout << node << " ";
                vis[node] = true;
            }
            cout << endl;
        }
    }

    return 0;
}