#include<bits/stdc++.h>
#define rep(i,a,b) for(int i=int(a),_=int(b);i<=_;++i)
#define per(i,a,b) for(int i=int(a),_=int(b);i>=_;--i)
using namespace std;
const int N=1e6+10,inf=2e9;
int n,K,D,h[N],t[N],mx[N],b[N],rem[N],c[N],dp[N],tot,rt[N],ch[4*N][2],res[4*N];
#define ls ch[x][0]
#define rs ch[x][1]
#define md ((l+r)>>1)
inline void pushup(int x){res[x]=max(res[ls],res[rs]);}
void build(int &x,int l,int r){
	if(!x)x=++tot;
	res[x]=-inf;
	if(l!=r)build(ls,l,md),build(rs,md+1,r);
}
void modify(int x,int l,int r,int y,int z){
	if(l==r){res[x]=z;return;}
	if(y<=md)modify(ls,l,md,y,z);
	else modify(rs,md+1,r,y,z);
	pushup(x);
}
int query(int x,int l,int r,int lx,int rx){
	if(l>=lx&&r<=rx)return res[x];
	int ans=-inf;
	if(lx<=md)ans=max(ans,query(ls,l,md,lx,rx));
	if(rx>md)ans=max(ans,query(rs,md+1,r,lx,rx));
	return ans;
}
int main(){
	scanf("%d%d%d",&n,&K,&D);
	rep(i,0,n-1)scanf("%d",&h[i]);
	rep(i,0,n-2)scanf("%d",&t[i]),t[i]+=i;
	rep(i,0,n-1)b[i]=i/K,rem[i]=i-b[i]*K,c[rem[i]]=b[i];
	rep(i,0,K-1)build(rt[i],0,c[i]);
	build(rt[K],0,n-1);
	per(i,n-1,0){
		if(i==n-1){
			dp[i]=h[i];
		}else{
			dp[i]=query(rt[K],0,n-1,i+1,t[i]);
			if(rem[i]&&b[i]<b[t[i]]){
				dp[i]=max(dp[i],D+mx[min(t[i],b[t[i]]*K+rem[i-1])]);
				if(b[i]<b[t[i]]-1)dp[i]=max(dp[i],D+query(rt[rem[i-1]],0,c[rem[i-1]],b[i]+1,b[t[i]]-1));
			}
			dp[i]+=b[i]*D+h[i];
		}
		modify(rt[K],0,n-1,i,dp[i]-b[i]*D);
		if(!rem[i]){
			int r=min(n,i+K)-1;
			rep(j,i,r)mx[j]=dp[j]-b[j]*D;
			rep(j,i+1,r)mx[j]=max(mx[j],mx[j-1]);
			rep(j,i,r)modify(rt[j-i],0,c[j-i],b[i],mx[j]);
		}
	}
	printf("%d\n",dp[0]);
	return 0;
}