//qoj906 tarjanSCC
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;

const int N = 5e5 + 10;
int n, m;
vector<int> g[N];
int dfn[N], low[N], cnt;
int ins[N], st[N], tp;

vector<int> scc[N];
int sct, siz[N];

void tg(int x){
	dfn[x] = low[x] = ++ cnt;
	ins[x] = 1;
	st[++tp] = x;
	for(int i : g[x]){
		if(!dfn[i]){
			tg(i);
			low[x] = min(low[x], low[i]);
		} else if(ins[i]){
			low[x] = min(low[x], dfn[i]);
		}
	}
	if(low[x] == dfn[x]){
		++ sct;
		while(st[tp] != x){
			++ siz[sct];
			scc[sct].push_back(st[tp]);
			ins[st[tp]] = 0;
			-- tp;
		}
		++ siz[sct];
		scc[sct].push_back(st[tp]);
		ins[st[tp]] = 0;
		-- tp;
	}
}

int main(){
	scanf("%d%d", &n, &m);
	for(int i = 1; i <= m; ++ i){
		int u, v;
		scanf("%d%d", &u, &v);
		++ u;
		++ v;
		g[u].push_back(v);
	}
	for(int i = 1; i <= n; ++ i){
		if(!dfn[i]){
			tg(i);
		}
	}
	printf("%d\n", sct);
	for(int i = sct; i >= 1; -- i){
		printf("%d ", siz[i]);
		for(int j : scc[i]){
			printf("%d ", j-1);
		}
		puts("");
	}
	return 0;
}