#include <iostream>
#include <cstdio>
#include <vector>
#include <stack>

using namespace std;

const int MAXN = 100005;

vector<int> g[MAXN];
vector<vector<int>> ctc;
stack<int> stiva;

int timp[MAXN], minim[MAXN], t;
bool inStiva[MAXN];

void dfs(int nod) {
    timp[nod] = minim[nod] = ++t;
    stiva.push(nod);
    inStiva[nod] = true;

    for (int vecin : g[nod]) {
        if (!timp[vecin]) {
            dfs(vecin);
            minim[nod] = min(minim[nod], minim[vecin]);
        }
        else if (inStiva[vecin])
            minim[nod] = min(minim[nod], timp[vecin]);
    }

    if (minim[nod] == timp[nod]) {
        vector<int> comp;
        while (true) {
            int element = stiva.top();
            stiva.pop();
            inStiva[element] = false;
            comp.push_back(element);
            if (element == nod) break;
        }
        ctc.push_back(comp);
    }
}

int main() {
    freopen("ctc.in", "r", stdin);
    freopen("ctc.out", "w", stdout);

    int n, m;
    cin >> n >> m;

    for (int i = 0; i < m; ++i) {
        int x, y;
        cin >> x >> y;
        g[x].push_back(y);
    }

    for (int i = 1; i <= n; ++i)
        if (!timp[i])
            dfs(i);

    cout << ctc.size() << "\n";

    for (auto& comp : ctc) {
        for (int x : comp)
            cout << x << " ";
        cout << "\n";
    }

    return 0;
}