rt

代码：

#include<bits/stdc++.h>
using namespace std;
const int slen=1e6+10;
int a[slen],u[slen];
int main()
{
  long long n,d,dis=0,ans=0,min=0,l;
  cin>>n>>d;
  for(int i=1;i<=n-1;++i)
    cin>>u[i];
  for(int i=1;i<=n;++i)
    cin>>a[i];
  for(int i=1;i<=n;++i)
  {
  	dis=dis+u[i];
  	if(a[i]<=a[1])
  	  ans=ans+(dis/d)*a[i];
  	l=n;
  }
  for(int i=l;i<=n;++i)
  {
  	dis=dis+u[i];
  	if(a[i]<a[i-1])
	{
	  min=a[i];
	  a[i]*(dis/min);
	  ans=ans+(dis/d)*a[i];
    }
  }
  cout<<ans;
  return 0;
}