#include    <fstream>
#include    <iostream>
#include    <vector>
#include    <stack>

using namespace std;
ifstream fin("ctc.in");
ofstream fout("ctc.out");
stack < int > S;
vector<int> G[100005],GT[100005],CTC[100005];
int N, M, NrCTC;
int beenThere[100005];
void Read()
{
    fin >> N >> M;
    for(int i = 1; i <= M; i++)
    {
        int x,y;
        fin >> x >> y;
        G[x].push_back(y);
        GT[y].push_back(x);
    }
}
void DFSP(int Nod)
{
    beenThere[Nod] = 1;
    for(unsigned int i=0; i<G[Nod].size();i++) {
        int Vecin = G[Nod][i];
        if(!beenThere[Vecin])
            DFSP(Vecin);
    }
    S.push(Nod);
}
void DFSM(int Nod)
{
    beenThere[Nod] = 2;
    CTC[NrCTC].push_back(Nod);
    for(unsigned int i=0; i<GT[Nod].size();i++) {
        int Vecin = GT[Nod][i];
        if(beenThere[Vecin]==1)
            DFSM(Vecin);
    }
}
void Solve()
{
    for(int i=1;i<=N;i++)
        if(!beenThere[i])
            DFSP(i);
    while(!S.empty()) {
        int Nod = S.top();
        cout << Nod << " ";
        if (beenThere[Nod] == 1) {
            NrCTC++;
            DFSM(Nod);
        }
        S.pop();
    }
}
void Print()
{
    fout << NrCTC <<"\n";
    for(int i = 1; i <= NrCTC; i++) {
        for(unsigned int j = 0; j < CTC[i].size(); j++)
            fout << CTC[i][j] <<" ";
        fout<<"\n";
    }
}
int main()
{
    Read();
    Solve();
    Print();
    return 0;
}