#include<bits/stdc++.h>
#define ffor(i,a,b) for(int i=(a);i<=(b);i++)
#define roff(i,a,b) for(int i=(a);i>=(b);i--)
using namespace std;
const int MAXN=500000+10;
int n,m,tot,in[MAXN],dfn[MAXN],low[MAXN];
stack<int> st;
vector<vector<int>> scc;
vector<int> G[MAXN];
void tarjan(int u) {
	dfn[u]=low[u]=++tot,in[u]=1,st.push(u);
	for(auto v:G[u]) {
		if(!dfn[v]) tarjan(v);
		else if(in[v]) low[u]=min(low[u],dfn[v]);
	}
	if(dfn[u]==low[u]) {
		vector<int> vc;
		while(st.top()!=u) vc.push_back(st.top()),in[st.top()]=0,st.pop();
		vc.push_back(u),st.pop(),scc.push_back(vc),in[u]=0;	
	}
	return ;
}
int main() {
	ios::sync_with_stdio(false),cin.tie(0),cout.tie(0);
	cin>>n>>m;
	ffor(i,1,m) {
		int u,v;
		cin>>u>>v,u++,v++;
		G[u].push_back(v);	
	}
	ffor(i,1,n) if(!dfn[i]) tarjan(i);
	reverse(scc.begin(),scc.end());
	cout<<scc.size()<<'\n';
	for(auto vc:scc) {
		cout<<vc.size()<<' ';
		for(auto id:vc) cout<<id-1<<' '; cout<<'\n';
	}
	return 0;
}