#include <bits/stdc++.h>

using namespace std;
vector <int> v[100001],inv[100001];
stack <int> stiva;
vector <int> componente[100001];
int viz[100001];
void DFS(int nod){
    viz[nod] = 1;
    for(auto x : v[nod]){
        if(!viz[x])
            DFS(x);
    }
    stiva.push(nod);
}
int nrctc;
void DFS1(int nod){
    viz[nod] = 2;
    componente[nrctc].push_back(nod);
    for(auto x : inv[nod]){
        if(viz[x] == 1){
            DFS1(x);
        }
    }
}
int main()
{
    ifstream cin("ctc.in");
    ofstream cout("ctc.out");
    int i,n,m;
    cin >> n >> m;
    for(i = 1;i <= m;i++){
        int x,y;
        cin >> x >> y;
        v[x].push_back(y);
        inv[y].push_back(x);
    }
    for(i = 1;i <= n;i++){
        if(!viz[i]){
            DFS(i);
        }
    }
    nrctc = 0;
    while(stiva.size()){
        i = stiva.top();
        stiva.pop();
        if(viz[i] == 1){
            nrctc++;
            DFS1(i);
        }
    }
    cout << nrctc << "\n";
    for(i = 1;i <= nrctc;i++){
        for(auto x : componente[i])
            cout << x << " ";
        cout << "\n";
    }
    return 0;
}