啊

#include <bits/stdc++.h>
using namespace std;
int s[1000005], v[1000005], q[1000005];

int main() {
	int n, d;
	cin >> n >> d;
	s[1] = 0;
	for (int i = 2; i <= n; i++) {
		int t;
		cin >> t;
		s[i] = t + s[i - 1];
	}
	for (int i = 1; i <= n; i++) {
		cin >> v[i];
	}
	int cnt = 1;
	q[1] = 1;
	for (int i = 2; i <= n; i++) {
		if (v[i] < v[q[cnt]]) {
			cnt++;
			q[cnt] = i;
		}
	}
	if (q[cnt] = n) {
		q[cnt++] = n;
	}
	int ans = 0, now = 0;
	for (int i = 1; i < cnt; i++) {
		int t = s[q[i + 1]] - s[q[i]];
		if (t < now) {
			now -= t;
		} else {
			t -= now;
			int tep = (t + d - 1) / d;
			ans += tep * v[q[i]];
			now = tep * d - t;
		}
	}
	cout << ans;
	return 0;
}