#include <iostream>
#include <fstream>
#include <vector>
#include <list>
#include <stack>
using namespace std;
ifstream f1 ("ctc.in");
ofstream f2 ("ctc.out");


vector<int> listaComponente[100005];
vector<int> deAfis[100005];
stack<int> componentVisitStack;
int index[100005], lowLink[100005], count=1, nr;
bool viz[100005];
int n,m,x,y;

void dfs(int nod){
    componentVisitStack.push(nod);
    viz[nod]=1;
    index[nod]=lowLink[nod]=count;
    count++;
    for(auto i : listaComponente[nod]){
        if(viz[i]==0){
            dfs(i);
            lowLink[nod]=min(lowLink[nod], lowLink[i]);
        }else{
            lowLink[nod]=min(lowLink[nod], lowLink[i]);
        }
    }

    if(index[nod] == lowLink[nod]){
        while(!componentVisitStack.empty()){
            deAfis[nr].push_back(componentVisitStack.top());
            if(index[componentVisitStack.top()]==lowLink[componentVisitStack.top()]){
                nr++;
                componentVisitStack.pop();
                break;
            }
            componentVisitStack.pop();
        }
    }
}

int main() {
    f1>>n>>m;
    for(int i=0;i<m;i++){
        f1>>x>>y;
        listaComponente[x].push_back(y);
    }
    dfs(1);
    f2<<nr<<endl;
    for(int i=0;i<nr;i++){
        for(int j : deAfis[i]){
            f2<<j<<" ";
        }
        f2<<endl;
    }
    return 0;
}