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

#define maxN 100100

using namespace std;

vector <int> G[maxN], GT[maxN], S[maxN], A;//G-graful initial GT -graful transpus
int N, M, T[maxN], Sol, Nr;
bitset <maxN> viz;

//parcugerea in adancime
void df (int x) 
{
    viz[x] = 1;
    for (int i = 0; i < (int) G[x].size(); ++ i)
        if (!viz[G[x][i]])
            df(G[x][i]);
    T[x] = ++ Nr;
}

//parcurgerea grafului transpus
void df2 (int x) 
{
    S[Sol].push_back(x);
    viz[x] = 1;
    for (int i = 0; i < (int) GT[x].size(); ++ i)
        if (!viz[GT[x][i]])
            df2(GT[x][i]);
}

inline bool cmp (int a, int b) {
    return T[a] > T[b];
}

int main () {
        int i, a, b, j;

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


    f>>N>>M;

    for (i = 1; i <= M; ++ i) {
        f>>a>>b;
        G[a].push_back(b);
        GT[b].push_back(a);
    }

    for (i = 1; i <= N; ++ i)
        if (!viz[i])
              df (i);

    for (i = 1; i <= N; ++ i)
        A.push_back(i);
      
    sort(A.begin(), A.end(), cmp);

    viz.reset ();

    for (i = 0; i < N; ++ i)
        if (!viz[A[i]]) {
            Sol ++;
            df2 (A[i]);      
        }
    g<<Sol<<"\n";

    for (i = 1; i <= Sol; ++ i) {
        for (j = 0; j < (int) S[i].size(); ++ j)
            g<<S[i][j]<<" ";
    g<<"";
    
    }
    f.close();
    g.close();
}