#include<bits/stdc++.h> using namespace std; int a[1000000],b[1000000]; int yuanliang(int x,int y) { if(x%y==0){return x/y;} else return x/y+1; } int main() { long long int n,d,sum,gongli=0,ans=0; cin>>n>>d; for(int i=1;i<=n-1;i++) cin>>a[i]; for(int i=1;i<=n;i++) cin>>b[i]; for(int i=1;i<=n;i++) if(b[i]<b[i+1]) b[i+1]=b[i]; for(int i=1;i<=n-1;i++) { int seeyouagain=a[i]-gongli; sum=yuanliang(seeyouagain,d); gongli=0; ans+=sumb[i]; gongli+=sumd-seeyouagain; } cout<<ans; return 0; }