#include <fstream>
#include <vector>

using namespace std;

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

const int N_MAX = 1e5 + 5;
int N, M, use[N_MAX], v[N_MAX], k, NrConexe = 1;
vector <int> G[N_MAX], T[N_MAX], Com[N_MAX];

void DFS1(int node){
    use[node] = 1;
    for (int vecin : G[node])
        if (!use[vecin]){
            use[vecin] = 1;
            DFS1(vecin);
        }
    v[++k] = node;
}

void DFS2(int node){
    use[node] = 2;
    Com[NrConexe].push_back(node);
    for (int vecin : T[node]){
        if (use[vecin] == 1){
            DFS2(vecin);
        }
    }
}

int main()
{
    in >> N >> M;
    for (int i = 1; i <= M; ++i){
        int x, y; in >> x >> y;
        G[x].push_back(y);
        T[y].push_back(x);
    }
    for (int i = 1; i <= N; ++i)
        if (!use[i]){
            DFS1(i);
        }
    for (int i = k; i >= 1; --i){
        if (use[v[i]] == 1){
            DFS2(v[i]);
            NrConexe++;
        }
    }
    out << NrConexe-1 << '\n';
    for (int i = 1; i <= NrConexe; out << '\n', ++i)
        for (int ceva : Com[i])
            out << ceva << " ";

    return 0;
}