#include <bits/stdc++.h>
using namespace std;
#define int long long
const int N=1e6+10;
int n,k,arr[N],brr[N],ans;
bool check(int x){
	int cnt=0,p=0;
	for(int i=1;i<=n;i++){
		cnt+=max(p,(arr[i]*brr[i]-x+brr[i]-1)/brr[i]);
	}
	return cnt<=k;
}
bool cmp(int x,int y){
	return x>y;
}
signed main(){
	cin>>n>>k;
	for(int i=1;i<=n;i++){
		cin>>arr[i];
	}
	for(int i=1;i<=n;i++){
		cin>>brr[i];
	}
	sort(arr+1,arr+1+n);
	sort(brr+1,brr+1+n,cmp);
	int l=0,r=N*N;
	while(l<=r){
		int mid=(r+l)>>1;
		if(check(mid)){
			r=mid-1;
			ans=mid;
		}else{
			l=mid+1;
		}
	}
	cout<<ans;
	return 0;
}

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MTEgMTQKMyAxIDQgMSA1IDkgMiA2IDUgMyA1CjggOSA3IDkgMyAyIDMgOCA0IDYgMg==

11 14
3 1 4 1 5 9 2 6 5 3 5
8 9 7 9 3 2 3 8 4 6 2