#include<bits/stdc++.h>
using namespace std;
const int N=5e5+10;
vector<int>G[N],G2[N];
int dfn[N],low[N],scc[N],tsp,cnt,siz[N];
stack<int>stk;bool instk[N];
void tarjan(int x)
{
	dfn[x]=low[x]=++tsp;
	stk.push(x);instk[x]=1;
	for(int y:G[x])
	{
		if(!dfn[y])
		{
			tarjan(y);
			low[x]=min(low[x],low[y]);
		}
		else if(instk[y])low[x]=min(low[x],dfn[y]);
	}
	if(dfn[x]==low[x])
	{
		cnt++;
		int z=-1;
		while(z!=x)
		{
			z=stk.top(),stk.pop(),instk[z]=0;
			scc[z]=cnt;siz[cnt]++;G2[cnt].push_back(z);
		}
	}
}
int main()
{
	int n,m;cin>>n>>m;
	for(int i=1;i<=m;i++)
	{
		int x,y;cin>>x>>y;x++,y++;
		G[x].push_back(y);
	}
	for(int i=1;i<=n;i++)if(!dfn[i])tarjan(i);
	cout<<cnt<<'\n';
	for(int i=cnt;i>=1;i--)
	{
		cout<<siz[i]<<' ';
		for(int y:G2[i])cout<<y-1<<' ';
		cout<<'\n';
	}
	return 0;
}

#include<bits/stdc++.h>
using namespace std;
const int N = 5e5 + 10;
int dfn[N], low[N], scc[N], tsp = 0, cnt = 0, siz[N];
vector<int> G[N], ring[N];
stack<int> stk; bool instk[N];

void tarjan(int x)
{
    dfn[x] = low[x] = ++tsp;
    stk.push(x); instk[x] = 1;
    for (auto y : G[x])
    {
        if (!dfn[y])
        {
            tarjan(y);
            low[x] = min(low[x], low[y]);
        }
        else if (instk[y]) low[x] = min(low[x], dfn[y]);
    }
    if (low[x] == dfn[x])
    {
        cnt ++;
        int z = -1;
        while (z != x)
        {
            z = stk.top(); stk.pop(); instk[z] = 0;
            scc[z] = cnt; siz[cnt] ++;
            ring[cnt].push_back(z);
        }
    }
}

int main()
{
    int n, m; cin >> n >> m;
    for (int i = 1; i <= m; i++)
    {
        int x, y; cin >> x >> y;
        x ++; y ++;
        G[x].push_back(y);
    }
    for (int i = 1; i <= n; i++) if (!dfn[i]) tarjan(i);
    cout << cnt << '\n';
    for (int i = cnt; i >= 1; i--)
    {
        cout << siz[i] << ' ';
        for (auto j : ring[i]) cout << j - 1 << ' ';
        cout << endl;
    }
    return 0;
}