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

#define debug(x) cerr << #x << " = " << x << "\n"
#define all(x) (x).begin(),(x).end()
#define len(x) (x).length()
#define sqr(x) (x) * (x)

using ull = unsigned long long;
using ll = long long;
using pii = pair<int, int>;
using pll = pair<ll, ll>;

template <typename T>
ostream& operator<<(ostream &os, const vector<T> &v) { os << '{'; string sep; for (const auto &x : v) os << sep << x, sep = ", "; return os << '}'; }
template <typename A, typename B>
ostream& operator<<(ostream &os, const pair<A, B> &p) { return os << '(' << p.first << ", " << p.second << ')'; }

const int INF = INT_MAX;
const int MOD = 1e9 + 7;
const double EPS = 1e-9;
const double PI = acos(-1);

ll t, n;

struct graph {
    vector<vector<int>> out, in;
    vector<bool> mark;
    vector<int> ord, comp;
    vector<vector<int>> ans;

    graph(int n = 0) {
        out.resize(n + 1);
        in.resize(n + 1);
        mark.resize(n + 1, false);
        comp.resize(n + 1, -1);
        ans.resize(n + 1);
    }

    void add(int from, int to) {
        out[from].push_back(to);
        in[to].push_back(from);
    }

    void dfs_ord(int node) {
        if (mark[node]) return;
        mark[node] = true;

        for (auto next: out[node])
            dfs_ord(next);

        ord.push_back(node);
    }

    void dfs_comp(int node, int c) {
        if (comp[node] != -1) return;
        comp[node] = c;
        ans[c].push_back(node);
        for (auto next: in[node])
            dfs_comp(next, c);
    }
};

int main(){
    ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
    mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
    ifstream cin("ctc.in");
    ofstream cout("ctc.out");

    int m, from, to;
    cin >> n >> m;
    graph g(n);
    for (int i = 0; i < m; i++) {
        cin >> from >> to;
        g.add(from, to);
    }

    // Make an order list of nodes,
    for (int i = 1; i <= n; i++)
        g.dfs_ord(i);
    g.mark.assign(n + 1, false);

    // Find out the components
    int c = 1;
    for (int i = n - 1; i >= 0; i--) {
        if (g.comp[g.ord[i]] == -1) {
            g.dfs_comp(g.ord[i], c);
            c++;
        }
    }

    cout << --c << '\n';
    for (int i = 1; i <= c; i++) {
        for (auto v: g.ans[i])
            cout << v << " ";
        cout << "\n";
    }

    return 0;
}