题解 100% AC

#include<bits/stdc++.h>
using namespace std;
int n,d,v[100010],a[100010],minx=INT_MAX;
long long sum,ans,pre;
int main(){
    freopen("road.in", "r", stdin);
    freopen("road.out", "w", stdout);
    cin>>n>>d;
    for(int i=2;i<=n;i++)cin>>v[i];
    for(int i=1;i<=n;i++)cin>>a[i];
    for(int i=2;i<=n;i++){
    	sum+=v[i];
        minx=min(minx,a[i-1]);
        long long tmp=max(0LL,(sum-pre+d-1)/d);
        ans+=tmp*minx;
        pre+=tmp*d;
    }
    cout<<ans;
    fclose(stdin);
    fclose(stdout);
	return 0;
}