rt，不知道为啥挂了 30pts /ll /kk /kel

#include <bits/stdc++.h>

typedef long long ll;

using namespace std;

const int MAXN = 1e5 + 10;

/*
一眼贪心，鉴定为：纯纯的暴力。 
*/

int n, m;

ll ans, x, y, a[MAXN], b[MAXN];

int main() {
//	freopen("road.in", "r", stdin);
//	freopen("road.out", "w", stdout);
	scanf("%d%d", &n, &m);
	for (int i = 2; i <= n; i++) scanf("%lld", &a[i]), a[i] += a[i - 1];
	for (int i = 1; i <= n; i++) scanf("%lld", &b[i]); b[n] = 0;
	for (int i = 2, k = 1; i <= n; i++) {
		if (b[i] >= b[k]) continue; y = a[i] - a[k];
		if (x < y) y -= x, ans += (ll)ceil((long double)y / m) * b[k], x = m - y % m;
		else x -= y; k = i;
	}
	printf("%lld", ans);
}

/*
Register_int AK CSP

orz ZZP
orz MCW
orz CYZ
orz HHX
orz HYT
*/