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

ifstream fin("ctc.in");
ofstream fout("ctc.out");
std::vector<std::vector<int>> adj;
std::vector<int> indexes;
std::vector<bool> onStack;
std::vector<int> lowLink;
std::vector<int> stk;
std::vector<bool> visited;
std::vector<std::vector<int>> ans;
int n, m;
int idx;

void tarjan(int i) {
    indexes[i] = idx;
    lowLink[i] = idx;
    ++idx;
    stk.push_back(i);
    onStack[i] = true;

    for (auto nod : adj[i]) {
        if (indexes[nod] == -1) {
            tarjan(nod);
            lowLink[i] = min(lowLink[i], lowLink[nod]);
        } else if (onStack[nod]) {
            lowLink[i] = min(lowLink[i], indexes[nod]);
        }
    }

    if (indexes[i] == lowLink[i]) {
        std::vector<int> ans_minor;
        int x;
        do {
            x = stk.back();
            stk.pop_back();
            onStack[x] = false;
            ans_minor.push_back(x);
        } while (x != i);

        ans.push_back(std::move(ans_minor));
    }
}

int main() {
    fin >> n >> m;
    adj.resize(n+1);
    visited.resize(n+1);
    indexes.resize(n+1);
    for (int i = 1; i <= n; ++i) indexes[i] = -1;
    onStack.resize(n+1);
    lowLink.resize(n+1);
    int x, y;
    while (m--) {
        fin >> x >> y;
        adj[x].push_back(y);
    }

    for (int i = 1; i <= n; ++i) {
        if (indexes[i] == -1) {
            tarjan(i);
        }
    }

    fout << ans.size() << '\n';
    for (auto& vec : ans) {
        for (auto elem : vec) {
            fout << elem << ' ';
        }
        fout << '\n';
    }

    return 0;
}