#include<bits/stdc++.h>
#define N 500010
#define pii pair<int,int>
#define fi first
#define se second
#define For(i,a,b) for(register int i=a;i<=b;i++)
using namespace std;
int n,m,x[N],y[N],dfn[N],low[N],cnt;
bool cut[N],vis[N];
vector<pii> go[N];
vector<int> h[N];
inline void tarjan(int x,int lst)
{
    dfn[x]=low[x]=++dfn[0];
    for(pii e:go[x]) if(e.se^lst)
    {
        int to=e.fi;
        if(!dfn[to]) tarjan(to,e.se^1),low[x]=min(low[x],low[to]);
        else low[x]=min(low[x],dfn[to]);
        if(low[to] > dfn[x]) cut[e.se>>1]=true;
    }
    return;
}

inline void dfs(int x,int id)
{
    vis[x]=true,h[id].push_back(x);
    for(pii e:go[x]) if(!vis[e.fi] && !cut[e.se>>1])
        dfs(e.fi,id);
    return;
}

int main()
{
    ios::sync_with_stdio(false);
    cin>>n>>m;
    For(i,1,m)
    {
        cin>>x[i]>>y[i];x[i]++,y[i]++;
        go[x[i]].push_back(pii(y[i],i<<1));
        go[y[i]].push_back(pii(x[i],i<<1|1));
    }For(i,1,n) if(!dfn[i]) tarjan(i,0);
    For(i,1,n) if(!vis[i]) dfs(i,++cnt);
    cout<<cnt<<'\n';
    For(i,1,cnt)
    {
        cout<<h[i].size()<<' ';
        for(int x:h[i]) cout<<x-1<<' ';
        cout<<'\n';
    }
    return 0;
}