#include <bits/stdc++.h>

using namespace std;

#define ll long long
#define ull unsigned ll
#define vec vector
#define flist forward_list
#define um unordered_map
#define us unordered_set
#define prioq priority_queue
#define all(x) x.begin(), x.end()
#define pb push_back
#define pf push_front
#define fi first
#define se second
#define ld long double
#define pll pair<ll, ll>
#define tll tuple<ll, ll, ll>
#define ass assign

#define LL_MAX LLONG_MAX
#define LL_MIN LLONG_MIN
#define ULL_MAX ULLONG_MAX
#define LD_MAX LDBL_MAX
#define LD_MIN LDBL_MIN

#define nl '\n'

#define vv(type, name, n, ...) vector<vector<type>> name(n, vector<type>(__VA_ARGS__))
#define vvv(type, name, n, m, ...)                                                                                     \
    vector<vector<vector<type>>> name(n, vector<vector<type>>(m, vector<type>(__VA_ARGS__)))

// https://trap.jp/post/1224/
#define rep1(n) for(ll i=0; i<(ll)(n); ++i)
#define rep2(i,n) for(ll i=0; i<(ll)(n); ++i)
#define rep3(i,a,b) for(ll i=(ll)(a); i<(ll)(b); ++i)
#define rep4(i,a,b,c) for(ll i=(ll)(a); i<(ll)(b); i+=(c))
#define cut4(a,b,c,d,e,...) e
#define rep(...) cut4(__VA_ARGS__,rep4,rep3,rep2,rep1)(__VA_ARGS__)
#define rep1e(n) for(ll i=1; i<=(ll)(n); ++i)
#define rep2e(i,n) for(ll i=1; i<=(ll)(n); ++i)
#define rep3e(i,a,b) for(ll i=(ll)(a); i<=(ll)(b); ++i)
#define rep4e(i,a,b,c) for(ll i=(ll)(a); i<=(ll)(b); i+=(c))
#define repe(...) cut4(__VA_ARGS__,rep4e,rep3e,rep2e,rep1e)(__VA_ARGS__)
#define per1(n) for(ll i=((ll)n)-1; i>=0; --i)
#define per2(i,n) for(ll i=((ll)n)-1; i>=0; --i)
#define per3(i,a,b) for(ll i=((ll)a)-1; i>=(ll)(b); --i)
#define per4(i,a,b,c) for(ll i=((ll)a)-1; i>=(ll)(b); i-=(c))
#define per(...) cut4(__VA_ARGS__,per4,per3,per2,per1)(__VA_ARGS__)
#define per1e(n) for(ll i=((ll)n); i>=1; --i)
#define per2e(i,n) for(ll i=((ll)n); i>=1; --i)
#define per3e(i,a,b) for(ll i=((ll)a); i>=(ll)(b); --i)
#define per4e(i,a,b,c) for(ll i=((ll)a); i>=(ll)(b); i-=(c))
#define pere(...) cut4(__VA_ARGS__,per4e,per3e,per2e,per1e)(__VA_ARGS__)
#define rep_subset(i,s) for(ll i=(s); i>=0; i=(i==0?-1:(i-1)&(s)))
// #define forit(v) for (auto it = v.begin(); it != v.end(); it++)
// #define forit2(it, v) for (auto it = v.begin(); it != v.end(); it++)
// #define forrit(v) for (auto it = v.rbegin(); it != v.rend(); it++)
// #define forrit2(it, v) for (auto it = v.rbegin(); it != v.rend(); it++)

// #ifdef i_am_noob
#define bug(...) cerr << "#" << __LINE__ << ' ' << #__VA_ARGS__ << "- ", _do(__VA_ARGS__)
template<typename T> void _do(vector<vector<T>> x){cerr << "\n"; for(auto i: x) {for(auto j : i) {cerr << j << ' ';} cerr << "\n";}}
template<typename T> void _do(vector<T> x){for(auto i: x) cerr << i << ' ';cerr << "\n";}
template<typename T> void _do(set<T> x){for(auto i: x) cerr << i << ' ';cerr << "\n";}
template<typename T> void _do(unordered_set<T> x){for(auto i: x) cerr << i << ' ';cerr << "\n";}
template<typename T> void _do(T && x) {cerr << x << endl;}
template<typename T, typename ...S> void _do(T && x, S&&...y) {cerr << x << ", "; _do(y...);}
// #else
// #define bug(...) 777771449
// #endif

const ll MOD = 1e9 + 7;
const ll INF = (1ll << 59);

const string FILENAME = "ctc";
ifstream fin(FILENAME + ".in");
ofstream fout(FILENAME + ".out");

#define cin fin
#define cout fout

class Graph
{
public:

	ll n;
	vec<flist<ll>> adj;
	
	void read();
	void dfs(ll u, vec<bool>& vis, vec<ll>& id, ll& cid, stack<ll>& visStack, vec<ll>& low, vec<bool>& done, list<list<ll>>& sccs);
	void findSccs();
};

int main()
{
	Graph g;
	g.read();
	g.findSccs();
	
    return 0;
}

void Graph::dfs(ll u, vec<bool>& vis, vec<ll>& id, ll& cid, stack<ll>& visStack, vec<ll>& low, vec<bool>& done, list<list<ll>>& sccs)
{
	vis[u] = 1;
	id[u] = cid++;
	low[u] = id[u];
	visStack.push(u);
	
	for(auto v : adj[u])
	{
		if(done[v]) continue;
		if(!vis[v]) dfs(v, vis, id, cid, visStack, low, done, sccs);
		low[u] = min(low[u], low[v]);
	}
	
	if(low[u] == id[u])
	{
		sccs.pb({});
		while(!visStack.empty() && visStack.top() != u)
		{
			sccs.back().pb(visStack.top());
			done[visStack.top()] = 1;
			visStack.pop();
		}
		
		done[u] = 1;
		sccs.back().pb(u);
		visStack.pop();
	}
}
void Graph::findSccs()
{
	ll cid = 0;
	vec<ll> id(n), low(n);
	vec<bool> vis(n, 0), done(n, 0);
	list<list<ll>> sccs;
	stack<ll> visStack;
	
	auto ldfs = [&](ll u, auto&& ldfs) -> void
	{
		vis[u] = 1;
		id[u] = cid++;
		low[u] = id[u];
		visStack.push(u);
		
		for(auto v : adj[u])
		{
			if(done[v]) continue;
			if(!vis[v]) ldfs(v, ldfs);
			low[u] = min(low[u], low[v]);
		}
		
		if(low[u] == id[u])
		{
			sccs.pb({});
			while(!visStack.empty() && visStack.top() != u)
			{
				sccs.back().pb(visStack.top());
				done[visStack.top()] = 1;
				visStack.pop();
			}
			
			done[u] = 1;
			sccs.back().pb(u);
			visStack.pop();
		}
	};
	
	rep(n) if(!vis[i]) ldfs(i, ldfs);
	
	cout << sccs.size() << nl;
	
	for(auto& scc : sccs)
	{
		for(auto& u : scc)
		{
			cout << u+1 << ' ';
		}
		cout << nl;
	}
}
void Graph::read()
{
	ll m;
	cin >> n >> m;
	adj.resize(n);
	rep(m)
	{
		ll a, b;
		cin >> a >> b;
		a--, b--;
		adj[a].pf(b);
	}
}