一道非常简单，被大佬们秒杀的一道普及题，我........

#include <iostream>
#include <algorithm>
#include <cstdio>
#include <cmath>
#include <vector>
using namespace std;
int main() {
    unsigned long long n = 0, d = 0, i = 0, j = 0;
    int v[100005] = { 0 }, a[100005] = { 0 };
    unsigned long long co = 0, mi = 0, tot = 0, nd = 0, cr = 0;
    cin >> n >> d;
    for (i = 1; i <= n - 1; ++i)
    {
        cin >> v[i];
    }
    for (i = 1; i <= n; ++i)
    {
        cin >> a[i];
    }
    mi = a[1];
    for (i = 1; i < n; ++i) {
        cr += v[i];
        while (cr > 0) {
            nd = (cr - 1) / d + 1;
            co = nd * mi;
            tot += co;
            cr -= nd * d;
            if (a[i + 1] < mi) 
                mi = a[i + 1];
        }
    }
    cout << tot << endl;
    return 0;
}