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

#define NMAX 100002

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

vector<int> graf[NMAX];
vector<int> SCC[NMAX];

int ind[NMAX], lowlink[NMAX];

bitset<NMAX> inStack;

stack<int> stiva;

int nrSCC = 0;

void getSCC(int node) {

    int x;
    do {
        x = stiva.top();
        stiva.pop();
        inStack[x] = 0;
        SCC[nrSCC].push_back(x);
    }while(x != node);

    nrSCC++;
}

int idx = 0;

void DFS(int node) {

    lowlink[node] = ind[node] = ++idx;

    stiva.push(node);
    inStack[node] = 1;

    for (auto& adj: graf[node]) {

        if (!ind[adj]) {
            DFS(adj);
            lowlink[node] = min(lowlink[node], lowlink[adj]);
        }
        else
            lowlink[node] = min(lowlink[node], ind[adj]);
    }

    if (lowlink[node] == ind[node])
        getSCC(node);
}

int main() {

    int N, M;

    fin >> N >> M;

    int x, y;
    while (M--) {

        fin >> x >> y;
        graf[x].push_back(y);
    }

    for (int i = 1; i <= N; ++i) {
        if (!ind[i])
            DFS(i);
    }

    fout << nrSCC << "\n";

    for (int i = 0; i < nrSCC; ++i) {
        for (auto& node: SCC[i])
            fout << node << " ";
        fout << "\n";
    }

    return 0;
}