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

using namespace std;

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

int n, m, a, b, nrCtc, k;
int low[DIM], niv[DIM];

bitset <DIM> f, prezentStiva;

stack <int> stec;

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

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

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