蒟蒻求大佬之调，源码在此

#include <bits/stdc++.h>
using namespace std;
const int N = 1e5+5;
int n, d;
int v[N], a[N];
int main(){
	cin >> n >> d;
	for(int i = 1; i < n; ++i){
		cin >> v[i];
	}
	for(int i = 1; i <= n; ++i){
		cin >> a[i];
	}
	long long ans = 0;
	int befStop = 1;
	long long V = 0;
	long long remaining = 0;
	for(int i = 1; i <= n; ++i){
		if(a[i] < a[befStop]){
			ans += a[befStop] * ceil((V * 1.0 - remaining) / d);
			remaining += ceil(V * 1.0 / d) * d - V;
			befStop = i;
			V = 0;
		}
		V += v[i];
	}
	ans += a[befStop] * ceil(V * 1.0 / d);
	cout << ans;
	return 0;
}