#include <bits/stdc++.h>
using namespace std;
const int N=5e5+10;
int dfn[N],low[N],stk[N],ins[N];
int col[N],top,tot,num;
vector<vector<int>> G,scc;
void tarjan(int x){
	stk[++top]=x;ins[x]=1;
	dfn[x]=low[x]=++tot;
	for (int v:G[x]){
		if (!dfn[v]) tarjan(v),low[x]=min(low[x],low[v]);
		else if (ins[v]) low[x]=min(low[x],dfn[v]);
	}if (dfn[x]==low[x]){
		int k;num++;
		do{
			k=stk[top--];col[k]=num;ins[k]=0;
		}while (k!=x);
	}return;
}
int main(){
	ios::sync_with_stdio(0);
	cin.tie(nullptr);cout.tie(nullptr);
	int n,m;cin>>n>>m;G.resize(n+10);
	for (int i=1;i<=m;i++){
		int u,v;cin>>u>>v;u++;v++;
		G[u].emplace_back(v);
	}for (int i=1;i<=n;i++){
		if (!dfn[i]) tarjan(i);
	}scc.resize(num+10);
	for (int i=1;i<=n;i++){
		scc[col[i]].emplace_back(i);
	}cout<<num<<endl;
	for (int i=num;i>=1;i--){
		cout<<scc[i].size()<<' ';
		for (int x:scc[i]) cout<<x-1<<' ';
		cout<<endl;
	}return 0;
}