哪个大佬帮帮本蒟蒻(50分RE)

#include<bits/stdc++.h>
#include<cstdio>
using namespace std;
long long a[10005],b[10005];
int main()
{
	//freopen("road.in","r",stdin) ;
	//freopen("road.out","w",stdout) ;
	long long n,d;
	cin>>n>>d;
	for(int i=1;i<n;i++){
		cin>>a[i];
	}
	for(int i=1;i<=n;i++){
		cin>>b[i];
	}
	long long ans=0;
	long long m=b[1],res=0;
	for(int i=1;i<n;i++){
		m=min(m,b[i]);
		if(res>=a[i]) res-=a[i];
		else{
			int t=(a[i]-res)/d;
			if ((a[i]-res)%d!=0) t++;
			ans+=m*t;
			res=t*d+res-a[i];
		}
	}
	cout<<ans;
	return 0;
}