#include<bits/stdc++.h>
using namespace std;
#ifdef DEBUG
#include"debug.h"
#else
#define debug(...) void()
#endif
#define all(x) (x).begin(),(x).end()
template<class T>
auto ary(T *a,int l,int r){
	return vector<T>{a+l,a+1+r};
}
using ll=long long;
using ull=unsigned long long;
const int N=2e5+10,M=2e5+10;
int n,m;
int kk=1,head[N];
struct edges{
	int to,nex;
}e[M*2];
void add(int u,int v){
	e[++kk]={v,head[u]},head[u]=kk;
	e[++kk]={u,head[v]},head[v]=kk;
}
int dft,sct,dfn[N],scc[N],low[N];
vector<int>pos[N];
void tarjan(int u,int las=-1){
	static int top,stk[N];
	dfn[u]=low[u]=++dft,stk[++top]=u;
	for(int i=head[u];i;i=e[i].nex)if(i^las^1){
		int v=e[i].to;
		if(!dfn[v])tarjan(v,i),low[u]=min(low[u],low[v]);
		else if(!scc[v])low[u]=min(low[u],dfn[v]);
	}
	if(dfn[u]==low[u]){
		sct++;
		do scc[stk[top]]=sct;while(stk[top--]^u);
	}
}
int main(){
	scanf("%d%d",&n,&m);
	for(int u,v;m--;){
		scanf("%d%d",&u,&v),add(u+1,v+1);
	}
	for(int i=1;i<=n;i++)if(!dfn[i])tarjan(i);
	for(int i=1;i<=n;i++)pos[scc[i]].push_back(i);
	printf("%d\n",sct);
	for(int i=1;i<=sct;i++){
		printf("%ld",pos[i].size());
		for(int u:pos[i])printf(" %d",u-1);
		puts("");
	}
	return 0;
}
#ifdef DEBUG
#include"debug.hpp"
#endif