#include <stdio.h>
#include <vector>
#include <stack>
#include <algorithm>
#define NMax 100010
using namespace std;

const char IN[]="ctc.in",OUT[]="ctc.out";

int N,M;
vector<int> ad[NMax];
vector<vector<int> > Sol;

void tarjan(int x){

	static vector<int> vec;
	static stack<int> st;
	static bool b[NMax],inStack[NMax];
	static int index,idx[NMax],low[NMax];

	int i;
	if (b[x]) return;
	idx[x]=low[x]=++index;
	st.push(x);b[x]=true;
	inStack[x]=true;

	for (i=0;i<(int)ad[x].size();++i) if (!low[ad[x][i]]){
		tarjan(ad[x][i]);
		low[x]=min(low[x],low[ad[x][i]]);
	} else if (inStack[ad[x][i]])
		low[x]=min(low[x],low[ad[x][i]]);

	if (idx[x]==low[x]){
		vec.clear();
		for (i=-1;i!=x;){
			i=st.top();st.pop();
			inStack[i]=false;
			vec.push_back(i);
		}
		Sol.push_back(vec);
	}

}

int main()
{
	int i,x,y;
	freopen(IN,"r",stdin);
	scanf("%d%d",&N,&M);
	while (M--)
		scanf("%d%d",&x,&y),
		ad[x].push_back(y);
	fclose(stdin);

	for (i=1;i<=N;++i) tarjan(i);
	for (i=0;i<(int)Sol.size();++i) sort(Sol[i].begin(),Sol[i].end());

	freopen(OUT,"w",stdout);
	printf("%d\n",Sol.size());
	for (i=0;i<(int)Sol.size();++i,printf("\n"))
		for (int j=0;j<(int)Sol[i].size();++j)
			printf("%d ",Sol[i][j]);
	fclose(stdout);
	return 0;
}