#include <bits/stdc++.h>
using namespace std;
 
int main() {
	int n,k;
	cin>>n>>k;
	vector<int> a(n),b(n);
	for(int i=0;i<n;++i) cin>>a[i];
	for(int i=0;i<n;++i) cin>>b[i];
	int ans=0;
	vector<pair<int,int>> vec;
	for(int i=0;i<n;++i) vec.push_back({b[i],a[i]});
	sort(vec.begin(),vec.end());
	for(int i=n-1;i>=0 && k>0;--i){
		if(k-vec[i].second>=0){
			ans+=vec[i].first*vec[i].second;
			k-=vec[i].second;
		} else{
			ans+=vec[i].first*k;
			k=0;
		}
	}
	cout<<ans;
 
	return 0;
}

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MyA2CjMgMSA2CjIgNyA0

3 6
3 1 6
2 7 4