// Problem: 13. 强连通分量
// URL: https://qoj.ac/contest/1536/problem/906
// Writer: WRuperD
// Powered by CP Editor (https://cpeditor.org)

#include<bits/stdc++.h>
using namespace std;
const long long inf = 1e18;
const int mininf = 1e9 + 7;
#define int long long
#define pb emplace_back
inline int read(){int x=0,f=1;char ch=getchar();while(ch<'0'||ch>'9'){if(ch=='-')f=-1;ch=getchar();}while(ch>='0'&&ch<='9'){x=(x<<1)+(x<<3)+(ch^48);ch=getchar();}return x*f;}
inline void write(int x){if(x<0){x=~(x-1);putchar('-');}if(x>9)write(x/10);putchar(x%10+'0');}
#define put() putchar(' ')
#define endl puts("")
const int MAX = 5e5 + 10;

int dfn[MAX], clk, low[MAX];
int stc[MAX], topp;
int col[MAX];
bool ins[MAX];

int sccnum;
vector <int> g[MAX];
vector <int> ret[MAX];

void dfs(int u){
	dfn[u] = low[u] = ++clk;
	stc[++topp] = u;
	ins[u] = 1;
	// if(u == 6);
	for(int v : g[u]){
		if(!dfn[v]){
			dfs(v);
			low[u] = min(low[u], low[v]);
		}else if(ins[v])	low[u] = min(low[u], dfn[v]);
	}
	// if(u == 6)	write(low[u]), put(), write(dfn[u]), endl;
	if(low[u] == dfn[u]){
		// write(u), endl;
		sccnum++;
		while(stc[topp] != u){
			col[stc[topp]] = u;
			ret[sccnum].pb(stc[topp]);
			ins[stc[topp]] =  0;
			topp--;
		}
		ret[sccnum].pb(stc[topp]);
		ins[stc[topp]] =  0;
		col[u] = u;
		topp--;
	}
	return ;
} 

void solve(){
	int n = read(), m = read();
	for(int i = 1; i <= m; i++){
		int u = read() + 1, v = read() + 1;
		g[u].pb(v);
	}
	for(int i = 1; i <= n; i++) {
		if(!dfn[i]){
			dfs(i);
			// write(i), put(), write(topp), endl;
		}
	}
	// write(col[6]), endl;
	write(sccnum), endl;
	for(int i = 1; i <= sccnum; i++){
		write(ret[i].size()), put();
		for(int u : ret[i])	write(u - 1), put();
		endl;
	}
}

signed main(){
	int t = 1;
	while(t--)	solve();
	return 0;
}