#include<fstream>
#include<algorithm>
#include<vector>
#include<stack>
#define pb push_back
using namespace std;
ifstream fin("ctc.in");
ofstream fout("ctc.out");
const int DN=1e5+5;
int n,m,f,g,niv[DN],low[DN],nr,instk[DN],cnt;
vector<int>v[DN],r[DN];
stack<int>stk;
void dfs(int nod)
{
	niv[nod]=low[nod]=++nr;
	stk.push(nod);
	instk[nod]=1;
	for(auto i:v[nod])
		if(niv[i])
		{
			if(instk[i])
				low[nod]=min(low[nod],low[i]);
		}
		else
		{
			dfs(i);
			low[nod]=min(low[nod],low[i]);
		}
	if(niv[nod]==low[nod])
	{
		cnt++;
		while(1)
		{
			f=stk.top();
			stk.pop();
			instk[f]=0;
			r[cnt].pb(f);
			if(f==nod)
				break;
		}
	}
}
int main()
{
	fin>>n>>m;
	while(m--)
	{
		fin>>f>>g;
		v[f].pb(g);
	}
	for(int i=1;i<=n;i++)
		if(!niv[i])
			dfs(i);
	fout<<cnt<<'\n';
	for(int h=1;h<=cnt;h++)
	{
		for(auto i:r[h])
			fout<<i<<' ';
		fout<<'\n';
	}
}