#include<bits/stdc++.h>
#pragma GCC optimize("O1")
#define endl '\n'
#include <iostream>
#include <vector>
#include <map>
#include <set>
#include <iterator>
#include <list>
#include <array>
#include <math.h>
#include <algorithm>
#include <queue>
#include <unordered_set>
#define ll long long int

using namespace std;
void speed()
{
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
}
struct stick
{
    int h,pun,idx;
    stick(){};
    stick(int _h,int _pun,int _idx)
    {
        h = _h;
        pun = _pun;
        idx = _idx;
    }
};
struct hole
{
    int ost_dep;
    vector<int>solet;
    hole(){};
    hole(int _ost_dep,vector<int>_solet)
    {
        ost_dep = _ost_dep;
        solet = _solet;
    }
};
bool cmp_st(stick a,stick b)
{
    return a.h>b.h;
}
int main()
{
    speed();
    #ifdef ONLINE_JUDGE
    freopen("sticks.in", "r", stdin);
    freopen("sticks.out", "w", stdout);
    #endif
    int n,b;cin>>n>>b;
    vector<stick>pruchki;
    vector<hole>dupki;
    for(int i=0;i<n;i++)
    {
        int vis;
        cin>>vis;
        pruchki.push_back(stick(vis,0,i));
    }
    for(int i=0;i<n;i++)
    {
        int nak;cin>>nak;
        pruchki[i].pun=nak;
    }
    sort(pruchki.begin(),pruchki.end(),cmp_st);
    for(int i=0;i<n;i++)
    {
        bool used = false;
        for(auto &hole:dupki)
        {
            if(pruchki[i].h<=hole.ost_dep)
            {
                hole.ost_dep-=pruchki[i].h;
                hole.solet.push_back(pruchki[i].idx);
                used=true;
                break;
            }
        }
        if(!used)
        {
            hole dup;
            dup.ost_dep = b-pruchki[i].h;
            dup.solet.push_back(pruchki[i].idx);
            dupki.push_back(dup);
        }
    }
    cout<<dupki.size()<<endl;
    for(auto &hole:dupki)
    {
        cout<<hole.solet.size()<<" ";
        for(int i:hole.solet)
        {
            cout<<i+1<<" ";
        }
        cout<<endl;
    }
    return 0;
}