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

#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 fin("ctc.in");
	ofstream fout("ctc.out");


	fin>>N>>M;

	for (i = 1; i <= M; ++ i) {
		fin>>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]);
		}
	fout<<Sol<<"\n";

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

	}

	fin.close();
	fout.close();
}