#include <bits/stdc++.h>

using namespace std;

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

const int nmax = 100005;
int n, m, id[nmax], low[nmax], z;
bool inStack[nmax];
vector <int> G[nmax];
stack <int> s;
vector <vector <int> > ans;
void tarjan(int nod){
    id[nod] = low[nod] = ++z;
    s.push(nod);
    inStack[nod] = true;
    for (auto it : G[nod]){
        if (id[it] == 0){
            tarjan(it);
            low[nod] = min(low[nod], low[it]);
        }
        else{
            if (inStack[it]){
                low[nod] = min(low[nod], id[it]);
            }
        }
    }
    if (id[nod] == low[nod]){
        vector <int> aux;
        int snod;
        do{
            snod = s.top();
            inStack[snod] = false;
            s.pop();
            aux.push_back(snod);
        } while (snod != nod);
        ans.push_back(aux);
    }
}

int main(){
    fin >> n >> m;
    for (int i = 1; i <= m; ++i){
        int x, y;
        fin >> x >> y;
        G[x].push_back(y);
    }
    for (int i = 1; i <= n; ++i){
        if (id[i] == 0){
            tarjan(i);
        }
    }
    fout << ans.size() << "\n";
    for (int i = 0; i < ans.size(); ++i){
        for (int j = 0; j < ans[i].size(); ++j){
            fout << ans[i][j] << " ";
        }
        fout << "\n";
    }
    fin.close();
    fout.close();
    return 0;
}