#include<bits/stdc++.h>
#define ll long long
using namespace std;
const ll N=5e5;
ll read(){
	ll S=0,F=1;char ch=getchar();
	while(!isdigit(ch)){
		if(ch=='-')F*=-1;
		ch=getchar();
	}while(isdigit(ch)){
		S=(S<<3)+(S<<1)+(ch^48);
		ch=getchar();
	}return S*F;
}ll n,m,u,v,lts,tp,sta[N+10],vis[N+10],dfn[N+10],low[N+10],cnt,in[N+10];
ll buc[N+10],ind[N+10];queue<ll >que;
vector<ll >vs[N+10],to[N+10],tl[N+10];
void dfs(ll id){
	low[id]=dfn[id]=++cnt;
	sta[++tp]=id;vis[id]=1;
	for(ll i=0;i<to[id].size();i++){
		if(!dfn[to[id][i]]){
			dfs(to[id][i]);
			low[id]=min(low[id],low[to[id][i]]);
		}else if(vis[to[id][i]])low[id]=min(low[id],dfn[to[id][i]]);
	}if(low[id]==dfn[id]){
		lts++;do{
			vs[lts].push_back(sta[tp--]);
			vis[sta[tp+1]]=0;in[sta[tp+1]]=lts;
		}while(sta[tp+1]!=id);
	}return;
}int main(){
	n=read();m=read();
	while(m--){
		u=read()+1;v=read()+1;
//		swap(u,v);
		to[u].push_back(v);
	}for(ll i=1;i<=n;i++)if(!dfn[i])dfs(i);
	printf("%lld\n",lts);
	for(ll i=1;i<=lts;i++){
		for(ll j=1;j<=lts;j++)buc[j]=0;
		for(ll J=0;J<vs[i].size();J++){ll j=vs[i][J];
			for(ll k=0;k<to[j].size();k++)if(!buc[in[to[j][k]]]&&in[to[j][k]]!=i){
				buc[in[to[j][k]]]++;
				tl[i].push_back(in[to[j][k]]);
				ind[in[to[j][k]]]++;
			}
		}
	}for(ll i=1;i<=lts;i++)if(!ind[i])que.push(i);
	while(!que.empty()){
		ll x=que.front();que.pop();		
		printf("%lld ",vs[x].size());
		for(ll j=0;j<vs[x].size();j++)printf("%lld ",vs[x][j]-1);
		putchar('\n');for(ll j=0;j<tl[x].size();j++){
			ind[tl[x][j]]--;
			if(!ind[tl[x][j]])que.push(tl[x][j]);
		}
	}return 0;
}