#include <fstream>
#include <stack>
#include <vector>

using namespace std;

ifstream cin("ctc.in");
ofstream cout("ctc.out");

int n, m, q;
vector<int> g[100001], gt[100001], a[100001];
stack<int> s;
int v[100001];  // visited

void read() {
    int x, y;
    cin >> n >> m;

    while (m--) {
        cin >> x >> y;
        g[x].push_back(y);
        gt[y].push_back(x);
    }
}

void show() {
    for (int i = 1; i <= n; i++) {
        cout << "i: " << i << ": ";
        for (int j = 0; j < g[i].size(); j++) {
            cout << g[i][j] << ' ';
        }
        cout << '\n';
    }
}

void show2() {
    for (int i = 1; i <= n; i++) {
        for (int j = 0; j < gt[i].size(); j++) {
            cout << gt[i][j] << ' ';
        }
    }
}

void dfs(int x) {
    v[x] = 1;
    for (int i = 0; i < g[x].size(); i++) {
        if (v[g[x][i]] == 0) {
            dfs(g[x][i]);
        }
    }
    s.push(x);
}

void dfs2(int x) {
    v[x] = 2;
    a[q].push_back(x);
    for (int i = 0; i < gt[x].size(); i++) {
        if (v[gt[x][i]] == 1) {
            dfs2(gt[x][i]);
        }
    }
}

int main() {

    read();

    for (int i = 1; i < n; i++) {
        if (v[i] == 0) {
            dfs(i);
        }
    }

    
    while (!s.empty()) {
        if (v[s.top()]  == 1) {
            dfs2(s.top());
            q++;
        }
        else {
            s.pop();
        }
    }

    cout << q << '\n';

    for (int i = 0; i < q; i++) {
        for (int j = 0; j < a[i].size(); j++) {
            cout << a[i][j] << ' ';
        }
        cout << '\n';
    }
    return 0;
}