#include <fstream>
#include <vector>
#include <bitset>

using namespace std;
const int NMAX = 100002;

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

vector <vector <int>> v, inv;
bitset <NMAX> f;

vector <int> topo;
void dfs1(int start) { ///in care fm sortarea
    f[start] = 1;
    for(auto nod : v[start]) {
        if(!f[nod])
            dfs1(nod);
    }
    topo.push_back(start);
}
vector <vector <int>> ctc;
void dfs2(int start) {
    f[start] = 1;
    for(auto nod : inv[start]) {
        if(!f[nod])
            dfs2(nod);
    }
    ctc.back().push_back(start);
}
int main()
{
    int n, m;
    cin >> n >> m;
    v.resize(n + 1);
    inv.resize(n + 1);
    for(int i = 1; i <= m; i++) {
        int a, b;
        cin >> a >> b;
        v[a].push_back(b);
        inv[b].push_back(a);
    }
    for(int i = 1; i <= n; i++) {
        if(!f[i])
            dfs1(i);
    }
    f = 0;
    for(int i = topo.size() - 1; i >= 0; i--) {
        if(!f[topo[i]]) {
            ctc.push_back(vector <int>());
            dfs2(topo[i]);
        }
    }
    cout << ctc.size() << '\n';
    for(int i = 0; i < ctc.size(); i++) {
        for(auto var : ctc[i])
            cout << var << " ";
        cout << '\n';
    }
    return 0;
}