#include <iostream>
#include <fstream>
#include <vector>
#include <deque>
#define dMAX 100000

using namespace std;

int n, m, x, y, SSCs, id;
vector<int> graf[dMAX + 2];
int ID[dMAX + 2], lowlink[dMAX + 2];
bool onStack[dMAX + 2];
bool taken[dMAX + 2];
deque<int> myStack;
vector<int> SSC[dMAX + 2];

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

void DFS(int k) {
    myStack.push_back(k);
    onStack[k] = true;
    ID[k] = lowlink[k] = ++id;
    int i, j, newV;
    for (i = 0; i < graf[k].size(); i++) {
        newV = graf[k][i];
        if (ID[newV] == 0) DFS(newV);
        if (onStack[newV]) {
            lowlink[k] = min(lowlink[k], lowlink[newV]);
        }
    }
    int pVerif;
    if (ID[k] == lowlink[k]) {
        SSCs++;
        for (pVerif = myStack.back(); !myStack.empty();) {
            onStack[pVerif] = false;
            lowlink[pVerif] = ID[k];
            SSC[SSCs].push_back(pVerif);
            if (pVerif == k) break;
            myStack.pop_back();
            pVerif = myStack.back();
        }
        myStack.pop_back();
    }
}

void FindSSCs() {
    int i, j;
    for (i = 1; i <= n; i++) {
        if (ID[i] == 0) {
            DFS(i);
        }
    }
}

int main()
{
    int i, j;
    fin >> n >> m;
    for (i = 1; i <= m; i++) {
        fin >> x >> y;
        graf[x].push_back(y);
    }
    FindSSCs();
    fout << SSCs << '\n';
    for (i = 1; i <= SSCs; i++) {
        //fout << SSC[i].size() << ' ';
        for (j = 0; j < SSC[i].size(); j++) {
            fout << SSC[i][j] << ' ';
        }
        fout << '\n';
    }
    return 0;
}