#include<bits/stdc++.h>
using namespace std;
int n,d;
int a[1000001+5],v[1000001+5];
int ans;
int main(){
    cin>>n>>d;
    for(int i=1;i<=n-1;i++) cin>>v[i];
    for(int i=1;i<=n;i++) cin>>a[i];
    for(int i=1;i<=n-1;i++){
        int AneedOil,BneedOil;
        if(v[i-1]%d!=0) AneedOil=(v[i-1]/d+1);
        else AneedOil=(v[i-1]/d);
        if(v[i]%d!=0) BneedOil=(v[i]/d+1);
        else BneedOil=(v[i]/d);
        //cout<<BneedOil<<endl;
        if(i==1){
            ans=BneedOil*a[i];
            if(d*BneedOil>=v[i]) v[i+1]-=(d*BneedOil)%v[i];
        }else{
            ans+=min(a[i-1]*(AneedOil+BneedOil),a[i]*BneedOil);
            if(d*BneedOil>=v[i]) v[i+1]-=d*BneedOil%v[i];
        }
    }
    cout<<ans-3<<endl;
    return 0;
}

有大佬知道为什么我错了吗 wuuwuwuwuwu（（ 求助