#pragma GCC optimize("Ofast")
#include <bits/stdc++.h>

typedef long long ll;

const ll mod=1e9+7;

const int dx[] = {0, 1, 0, -1};
const int dy[] = {1, 0, -1, 0};
const int N=1e5+5;

#define all(x) x.begin(),x.end()
#define allr(x) x.rbegin(),x.rend()
#define rc(x)  return cout<<x<<"\n",0
#define sz(s)  (int) s.size()
#define pb push_back
#define mp make_pair
#define fr first
#define sc second
#define PI 3.14159265358979

using namespace std;

ll t,n,counter=1;


vector<int>g1[N];
vector<int>g2[N];
vector<pair<int,int>>fin(N);
ll viz[N];
ll viz2[N];
vector<int>rasp;
void dfs1(int i) {
	if(viz[i])return;
	viz[i]=1;
	for (auto it:g1[i]) {
		dfs1(it);
	}
	fin[i]={counter++,i};
}

void dfs2(int i) {
	if(viz2[i])return;
	viz2[i]=1;
	for (auto it:g2[i]) {
		dfs2(it);
	}
	rasp.pb(i);
}

int main() {
ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
	ifstream cin("ctc.in");
	ofstream cout("ctc.out");
	ll n,m;
	cin >> n >> m;
	vector<vector<int>>raspfinal;
	for (int i=1; i<=m; i++) {
		ll x,y;
		cin >> x >> y;
		g1[x].pb(y);
		g2[y].pb(x);
	}
	for (int i=1; i<=n; i++) {
		if (!viz[i]) {
			dfs1(i);
		}
	}
	ll ans=0;
	sort(all(fin));
	reverse(all(fin));
	for (auto it:fin) {
		if (it.sc==0)break;
		if (!viz2[it.sc]) {
			dfs2(it.sc);
			raspfinal.pb(rasp);
			ans++;
			rasp.clear();
		}	
	}
	cout << ans << '\n';
	for (auto it:raspfinal) {
		for (auto jt:it) {
			cout << jt << " ";
		}
		cout << '\n';
	}
	
}