#include <fstream>
#include <cstring>
#include <algorithm>
#include <vector>
#include <stack>
#include <climits>
using namespace std;

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

const int MAXN = 100005;
int n, m;
vector<int> v[MAXN];
bool viz[MAXN];
int low[MAXN];
int comp;
vector<int> sol[MAXN];
stack<int> s;
bool ons[MAXN];
int ind, lvl[MAXN];

void dfs(int k) {
    viz[k] = sol;
    low[k] = ++ind;
    lvl[k] = ind;
    s.push(k);
    ons[k] = 1;

    for (int i = 0; i < v[k].size(); ++i) {
        int node = v[k][i];
        if (viz[node] == 0) {
            dfs(node);
            low[k] = min(low[k], low[node]);
        }
        else if (ons[node] == 1) {
            low[k] = min(low[k], low[node]);
        }
    }

    if (low[k] == lvl[k]) {
        comp++;
        while (s.top() != k) {
            sol[comp].push_back(s.top());
            ons[s.top()] = 0;
            s.pop();
        }
        if (!s.empty()) {
            sol[comp].push_back(k);
            ons[k] = 0;
            s.pop();
        }
    }
}

int main() {

    fin >> n >> m;
    for (int i = 1; i <= m; ++i) {
        int x, y;
        fin >> x >> y;
        v[x].push_back(y);
    }

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

    fout << comp << '\n';
    for (int i = 1; i <= comp; ++i) {
        for (int j = 0; j < sol[i].size(); ++j) {
            fout << sol[i][j] << ' ';
        }
        fout << '\n';
    }

    fout.close();
    return 0;
}