#include <string>
#include <vector>
#include<iostream>
#include<cstdio>
#include<cstdlib>
#include<stack>
#include<queue>
#include<cmath>
#include<algorithm>
#include<functional>
#include<list>
#include<deque>
#include<bitset>
#include<set>
#include<map>
#include<unordered_map>
#include<unordered_set>
#include<cstring>
#include<sstream>
#include<complex>
#include<iomanip>
#include<numeric>
#include<cassert>
#include<random>
#define X first
#define Y second
#define pb push_back
#define rep(X,Y) for (int (X) = 0;(X) < (int)(Y);++(X))
#define reps(X,S,Y) for (int (X) = (int)(S);(X) < (int)(Y);++(X))
#define rrep(X,Y) for (int (X) = (int)(Y)-1;(X) >=0;--(X))
#define rreps(X,S,Y) for (int (X) = (int)(Y)-1;(X) >= (int)(S);--(X))
#define repe(X,Y) for ((X) = 0;(X) < (Y);++(X))
#define peat(X,Y) for (;(X) < (Y);++(X))
#define all(X) (X).begin(),(X).end()
#define rall(X) (X).rbegin(),(X).rend()
#define eb emplace_back
#define UNIQUE(X) (X).erase(unique(all(X)),(X).end())
#define Endl endl
#define NL <<"\n"
#define cauto const auto

using namespace std;
using ll=long long;
using pii=pair<int,int>;
using pll=pair<ll,ll>;
template<class T> using vv=vector<vector<T>>;
template<class T> inline bool MX(T &l,const T &r){return l<r?l=r,1:0;}
template<class T> inline bool MN(T &l,const T &r){return l>r?l=r,1:0;}
//#undef NUIP
#ifdef NUIP
#include "benri.h"
#else
#define out(args...)
#endif
#ifdef __cpp_init_captures
template<typename T>vector<T> table(int n, T v){ return vector<T>(n, v);}
template <class... Args> auto table(int n, Args... args){auto val = table(args...); return vector<decltype(val)>(n, move(val));}
#endif
template<class A,class B> pair<A,B> operator+(const pair<A,B> &p,const pair<A,B> &q){ return {p.X+q.X,p.Y+q.Y};}
template<class A,class B,class C,class D> pair<A,B>& operator+=(pair<A,B> &p,const pair<C,D> &q){ p.X+=q.X; p.Y+=q.Y; return p;}
template<class A,class B> pair<A,B> operator-(const pair<A,B> &p,const pair<A,B> &q){ return {p.X-q.X,p.Y-q.Y};}
template<class A,class B,class C,class D> pair<A,B>& operator-=(pair<A,B> &p,const pair<C,D> &q){ p.X-=q.X; p.Y-=q.Y; return p;}
template<class A,class B> istream& operator>>(istream &is, pair<A,B> &p){ is>>p.X>>p.Y; return is;}
template<class T=ll> T read(){ T re; cin>>re; return move(re);}
template<class T=ll> T read(const T &dec){ T re; cin>>re; return re-dec;}
template<class T=ll> vector<T> readV(const int sz){ vector<T> re(sz); for(auto &x:re) x=read<T>(); return move(re);}
template<class T=ll> vector<T> readV(const int sz, const T &dec){ vector<T> re(sz); for(auto &x:re) x=read<T>(dec); return move(re);}
vv<int> readG(const int &n,const int &m){ vv<int> g(n); rep(_,m){ cauto a=read<int>(); cauto b=read<int>(); g[a].pb(b); } return move(g);}
vv<int> readG(const int &n){ return readG(n,n-1);}
const ll MOD=1e9+7; //998244353

typedef vv<int> Graph;
struct Scc{
  stack<int> S;
  vector<int> inS,low,num;
  int time=0;
public:
  Graph dag;
  vector<int> inv;
  vv<int> scc;
  void visit(const Graph &g, int v){
    low[v] = num[v] = ++time;
    S.push(v); inS[v]=1;
    for(const int  &w:g[v]){
      if(!num[w]){
				visit(g,w);
				low[v]=min(low[v],low[w]);
      }else if(inS[w]) low[v]=min(low[v],num[w]);
    }
    if(low[v]==num[v]){
      scc.eb();
      while(1){
				int w = S.top(); S.pop(); inS[w]=0;
				scc.back().pb(w);
				if(v==w) break;
      }
    }
  }
  Scc(const Graph &g) {
    const int n = g.size();
    num.resize(n); low.resize(n); inS.resize(n);
    rep(u,n)if(!num[u]) visit(g,u);
    reverse(all(scc));
    
    // inv.resize(n); dag.resize(scc.size());
    // rep(i,scc.size())for(auto v:scc[i]) inv[v]=i;
    // rep(i,scc.size())for(auto v:scc[i])for(auto e:g[v])
		// 	if(inv[e]!=i)	dag[i].pb(inv[e]);
  }
};

int main(){
  ios_base::sync_with_stdio(false); cin.tie(0);
  cout<<fixed<<setprecision(0);
	cauto n=read();
	cauto m=read();
	cauto g=readG(n,m);
	Scc h(g);
	cauto &re=h.scc;
	cout<<re.size() NL;
	for(auto v:re){
		cout<<v.size();
		for(auto x:v) cout<<" "<<x;
		cout NL;
	}
  return 0;
}


Measured memory_bytes: 59832