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

const int maxim = 100002;
int n, m, intersectie[maxim], vizitate[maxim], ctc[maxim], nrComp = 0;
vector<int> a[maxim], transpus[maxim];

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, vector<int> graf[maxim]){
    vizitate[x] = 1;
    for(auto j: graf[x])
        if(vizitate[j] == 0)
            dfs(j, graf);
}

int main(){
    citireOrientat();
    for(int i = 1; i <= n; i++){
        if(ctc[i] == 0){
            nrComp++;
            dfs(i, a);
            for(int x = 1; x <= n; x++){
                intersectie[x] += vizitate[x];
                vizitate[x] = 0;
            }
            dfs(i, transpus);
            for(int x = 1; x <= n; x++){
                intersectie[x] += vizitate[x];
                vizitate[x] = 0;
            }
            for(int x = 1; x <= n; x++){
                if(intersectie[x] == 2)
                    ctc[x] = nrComp;
                intersectie[x] = 0;
            }
        }
    }
    out << nrComp << "\n";
    for(int i = 1; i <= nrComp; i++){
        for(int j = 1; j <= n; j++)
            if(ctc[j] == i)
                cout << j << " ";
        out << "\n";
    }
    return 0;
}