#include <bits/stdc++.h>
#define DIM 100005

using namespace std;

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

int n, m, i, j, x, y, nrCtc;
int f[DIM], isStec[DIM], low[DIM], niv[DIM];

vector <int> L[DIM], comp[DIM];

stack <int> stec;

void dfs (int nod){
    int vecin, don;
    f[nod] = 1;
    nrCtc++;
    low[nod] = niv[nod] = nrCtc;
    stec.push(nod);
    isStec[nod] = 1;
    for (int i=0; i<L[nod].size(); i++){
        vecin = L[nod][i];
        if (!f[vecin]){
            dfs(vecin);
            low[nod] = min (low[nod], low[vecin]);
        }
        else{
            if (isStec[vecin])
                low[nod] = min (low[nod], low[vecin]);
        }
    }
    if (low[nod] == niv[nod]){
        do{
            don = stec.top();
            stec.pop();
            isStec[don] = 0;
            comp[nrCtc].push_back(don);
        }while(don != nod);
    }
}

int main(){
    fin >> n >> m;
    for (i=1; i<=m; i++){
        fin >> x >> y;
        L[x].push_back(y);
    }
    for (i=1; i<=n; i++){
        if (!f[i]){
            dfs (i);
        }
    }
    int K;
    for (i=1; i<=nrCtc; i++){
        if (comp[i].size()){
            K++;
        }
    }
    fout << K << "\n";
    for (i=1; i<=nrCtc; i++){
        if (comp[i].size()){
            for (j=0; j<comp[i].size(); j++){
                fout << comp[i][j] << " ";
            }
            fout << "\n";
        }
    }
    return 0;
}