CCF的数据好水

#include<bits/stdc++.h>
#define MAXN int(1e5)+5
#define INF INT_MAX
typedef long long ll;
using namespace std;

ll n,d,mn=INF,v[MAXN],a,ans,s;
int main(){
    freopen("road.in","r",stdin);
    freopen("road.out","w",stdout);
    scanf("%lld%lld",&n,&d);
    for(ll i=1;i<n;i++)scanf("%lld",&v[i]);
    for(ll i=1;i<n;i++){
        scanf("%lld",&a);
        mn = min(mn,a);
        ans+=(((v[i]-s)/d)+((v[i]-s)%d!=0))*mn;
        s=(d-(v[i]-s)%d)%d;
    }
    scanf("%lld",&a);
    printf("%lld",ans);
    return 0;
}