#include <bits/stdc++.h>
using namespace std;
 
int n, m, tsort[100002], k, cnt;
vector <int> v[100002], inv[100002], sol[100002];
bool u[100002];
 
void dfs(int q){
    u[q] = 1;
    for (int i=0; i<v[q].size(); i++)
        if (!u[v[q][i]]) dfs(v[q][i]);
    tsort[++k] = q;
}
 
void dfsinv(int q){
    u[q] = 0;
    for (int i=0; i<inv[q].size(); i++)
        if (u[inv[q][i]]) dfsinv(inv[q][i]);
    sol[cnt].push_back(q);
}
 
int main(){
    ifstream cin ("ctc.in");
    ofstream cout ("ctc.out");
    cin >> n >> m;
    for (int i=1; i<=m; i++){
        int x, y;
        cin >> x >> y;
        v[x].push_back(y);
        inv[y].push_back(x);
    }
    for (int i=1; i<=n; i++){
        if (!u[i]) dfs(i);
    }
    for (int i=n; i>=1; i--)
        if (u[tsort[i]]) cnt++, dfsinv(tsort[i]);
    cout << cnt << "\n";
    for (int i=1; i<=cnt; i++){
        for (int j=0; j<sol[i].size(); j++) cout << sol[i][j] << " ";
        cout << "\n";
    }
    return 0;
}