#include<iostream>
#include<fstream>
#include<vector>
#include<bitset>
using namespace std;
ifstream in("ctc.in");
ofstream out("ctc.out");
#define MaxV 100005
vector<int> graf[MaxV], graft[MaxV];
bitset<MaxV> viz;
bitset<MaxV> viz2;
bitset<MaxV> eSol;
vector<int> sol;
bool transpus;
typedef vector<int>::iterator iter;
int nodi;
void dfs(int nod)
{
	if(nod < nodi)
		return;
	iter i;
	if(transpus == false)
	{
		viz[nod] = 1;
		for(i = graf[nod].begin(); i != graf[nod].end(); i++)
		{
			if(!eSol[*i] && viz[*i] == 0)
			{
				dfs(*i);
			}
		}
	}
	else
	{
		viz2[nod] = 1;
		if(viz[nod] == 1)
		{
			sol.push_back(nod);
			eSol[nod] = 1;
		}
		for(i = graft[nod].begin(); i != graft[nod].end(); i++)
		{
			if(!eSol[*i] && viz2[*i] == 0)
			{
				dfs(*i);
			}
		}
	}
}
int n,m;
int main()
{
	int i,x,y,nrSol = 0;
	in >> n >> m;
	for(i = 1; i <= m; i++)
	{
		in >> x >> y;
		graf[x].push_back(y);
		graft[y].push_back(x);
	}
	for(i = 1; i <= n; i++)
	{
		if(!eSol[i])
		{
			nodi = i;
			transpus = 0;
			viz.reset();
			dfs(i);
			
			transpus = 1;
			viz2.reset();
			dfs(i);
			
			nrSol++;
			sol.push_back(n + 1);
		}
	}
	out << nrSol;
	while(sol.begin() != sol.end())
	{
		if(*(sol.end() - 1) == n + 1)
			out << '\n';
		else
			out << *(sol.end() - 1) << ' ';
		sol.pop_back();
	}
}