#include<iostream>
#include<fstream>
#include<vector>
using namespace std;

const int maxim = 100002;
int n, m, pluss[maxim], minuss[maxim], parcurse[maxim];
vector<int> a[maxim], transpus[maxim], ctcActual;
vector<vector<int>> solutie;

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

void citireOrientat(){
    int x, y;
    in >> n >> m;
    for(int i = 1; i <= m; i++){
        in >> x >> y;
        a[x].push_back(y);
        transpus[y].push_back(x); //formez graful transpus
    }
}

void dfs(int x){
    pluss[x] = 1;
    for(auto j: a[x])
        if(pluss[j] == 0)
            dfs(j);
}

void dfsTranspus(int x){
    minuss[x] += (pluss[x] + 1);
    if(minuss[x] == 2){
        ctcActual.push_back(x);
        parcurse[x] = 1;
    }
    for(auto j: transpus[x])
        if(minuss[j] == 0)
            dfsTranspus(j);
}


int main(){
    citireOrientat();
    for(int i = 1; i <= n; i++){
        if(parcurse[i] == 0){
            dfs(i);
            dfsTranspus(i);

            for(int x = 1; x <= n; x++)
                pluss[x] = minuss[x] = 0;

            if(ctcActual.empty() == 0)
                solutie.push_back(ctcActual);
            ctcActual.clear();
        }
    }
    out << solutie.size() << "\n";
    for(auto i: solutie){
        for(auto j: i)
            out << j << " ";
        out << "\n";
    }
    return 0;
}