#include <fstream>
#include <vector>
#include <stack>

#define NMAX 100000

using namespace std;

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

int n, m, nrCTC;
int ver[NMAX + 1];
vector <int> gf[NMAX + 1], gft[NMAX + 1], rsp[NMAX + 1];
stack <int> ord;

void dfsp(int nc) {
    ver[nc] = 1;
    for (int j = 0; j < gf[nc].size(); j++)
        if (ver[gf[nc][j]] == 0)
            dfsp(gf[nc][j]);
    ord.push(nc);
}

void dfsm(int nc) {
    ver[nc] = 2;
    rsp[nrCTC].push_back(nc);
    for (int j = 0; j < gft[nc].size(); j++)
        if (ver[gft[nc][j]] == 1)
            dfsm(gft[nc][j]);
}

int main()
{
    fin >> n >> m;
    for (int i = 1; i <= m; i++) {
        int x, y;
        fin >> x >> y;
        gf[x].push_back(y);
        gft[y].push_back(x);
    }
    for (int i = 1; i <= n; i++)
        if (ver[i] == 0) {
            dfsp(i);
        }
    while (!ord.empty()) {
        int nc = ord.top();
        if(ver[nc] == 1) {
            nrCTC++;
            dfsm(nc);
        }
        ord.pop();
    }
    fout << nrCTC << '\n';
    for (int i = 1; i <= nrCTC; i++){
        for (int j = 0; j < rsp[i].size(); j++)
            fout << rsp[i][j] << ' ';
        fout << '\n';
    }
    return 0;
}