#include<iostream>
#include<set>
#include<vector>
using namespace std;
const int MAXN=10e+6;
struct f
{
	int ind,h,p;
};
struct C1
{
	int cmp(f f1,f f2) const
	{
		if(f1.p>f2.p)return 1;
		if(f1.p<f2.p)return -1;
		return f1.ind-f2.ind;
	}
	bool operator()(f f1,f f2) const
	{
		return cmp(f1,f2)<0;
	}
};
struct C2
{
	int cmp(f f1,f f2) const
	{
		if(f1.h<f2.h)return 1;
		if(f1.h>f2.h)return -1;
		return f1.ind-f2.ind;
	}	
	bool operator()(f f1,f f2) const
	{
		return cmp(f1,f2)<0;
	}
};
vector<vector<int>> res;
int n,b;
f inp[MAXN];
set<f,C1> s_p;
set<f,C2> s_h;
int main()
{
	freopen("sticks.in", "r", stdin);
	freopen("sticks.out", "w", stdout);
	cin>>n>>b;
	for(int i=0;i<n;i++)
	{
		inp[i].ind=i+1;
		cin>>inp[i].h;
	}
	for(int i=0;i<n;i++)
	{
		cin>>inp[i].p;
		s_p.insert(inp[i]);
		s_h.insert(inp[i]);
	}
	int k=0;
	while(s_p.size()>0)
	{
		if(k<=0)
		{
			res.push_back(vector<int>());
			k=b;
		}
		auto it=s_h.upper_bound(f{-1,k,-1});
		f tmp;
		if(it!=s_h.end())
		{
			tmp=*it;
			(*res.rbegin()).push_back(tmp.ind);
			s_h.erase(it);
			s_p.erase(tmp);
		}
		else
		{
			it=s_p.begin();
			tmp=*it;
			(*res.rbegin()).push_back(tmp.ind);
			s_h.erase(tmp);
			s_p.erase(it);
		}
		k-=tmp.h;
	}
	cout<<res.size()<<endl;
	for(auto p1:res)
	{
		cout<<p1.size()<<' ';
		for(int p2:p1)
			cout<<p2<<' ';
		cout<<endl;
	}
	return 0;
}
/*
7 9
3 4 1 8 4 7 3
3 2 6 10 5 3 3
*/