/*
#pragma GCC optimize("Ofast")
#pragma GCC target("avx2")
#pragma GCC optimize("unroll-loops")
*/
#include <bits/stdc++.h>
#define int long long
#define taskname "bai3"
#define all(x) x.begin(), x.end()
#define ll long long
#define ld long double
#define pb push_back
#define mp make_pair
#define ff first
#define ss second
#define pii pair<int, int>
#define vi vector<int>
using namespace std;

const int mxN = 1e5 + 5;
const int mod = 1e9 + 7;
const ll oo = 1e18;

int n, k, d, a[mxN], b[mxN], st[4 * mxN], dp[mxN];
vector<pii> segments;
set<pii> s[mxN];

bool sortbysec(pii x, pii y) {
	if(x.ss == y.ss) return (x.ff < y.ff);
	return (x.ss < y.ss);
}

void build(int l, int r, int idx) {
	if(l == r) {
		st[idx] = -oo;
		return;
	}
	int mid = (l + r) >> 1;
	build(l, mid, idx * 2);
	build(mid + 1, r, idx * 2 + 1);
	st[idx] = max(st[idx * 2], st[idx * 2 + 1]);
}


void update1(int l, int r, int idx, int pos, int val) {
	if(l == r) {
		st[idx] = val;
		return;
	}
	int mid = (l + r) >> 1;
	if(pos <= mid) update1(l, mid, idx * 2, pos, val);
	else update1(mid + 1, r, idx * 2 + 1, pos, val);
	st[idx] = max(st[idx * 2], st[idx * 2 + 1]);
}

int get(int l, int r, int idx, int u, int v) {
	if(v < u) return -oo;
	if(r < u || v < l) return -oo;
	if(u <= l && r <= v) {
		//cout << l << " " << r << " " << idx << " " << st[idx] << endl;
		return st[idx];
	}
	int mid = (l + r) >> 1;
	return max(get(l, mid, idx * 2, u, v), get(mid + 1, r, idx * 2 + 1, u, v));
}

void solve() {
	cin >> n >> k >> d;
	build(1, k, 1);
	for(int i = 1; i <= n; ++i) cin >> a[i];
	for(int i = 1; i < n; ++i) {
		cin >> b[i];
		segments.pb({i, i + b[i]});
	}
	sort(all(segments), sortbysec);

	dp[1] = a[1]; s[1 % k].insert({dp[1] + (1 / k) * d, 1});
	update1(1, k, 1, (1 % k) + 1, dp[1]);

	int idx = 0;
	for(int i = 2; i <= n; ++i) {
		while(idx + 1 < n && segments[idx].ss < i) {
			int i_ = segments[idx].ff;
			int tmp = i_ % k, tmp1 = i_ / k;
			s[tmp].erase({dp[i_] + tmp1 * d, i_});
			pii lst = {-oo, oo};
			if(!s[tmp].empty()) lst = *prev(s[tmp].end());
			update1(1, k, 1, tmp + 1, lst.ff);
			++idx;
		}

		int tmp = i % k, tmp1 = i / k;

		if(tmp1 < 1) {
			int get1 = get(1, k, 1, 1, tmp + 1);
			//cout << get1 << endl;
			get1 -= tmp1 * d;
			dp[i] = a[i] + get1;
		}
		else {
			int get1 = get(1, k, 1, 1, tmp + 1), get2 = get(1, k, 1, tmp + 2, k);
			get1 -= tmp1 * d;
			get2 -= (tmp1 - 1) * d;
			//cout << get1 << " " << get2 << endl;
 			dp[i] = a[i] + max(get1, get2);
		}

		//cout << "dp: " << i << " " << dp[i] << endl;

		s[tmp].insert({dp[i] + tmp1 * d, i});
		pii lst = *prev(s[tmp].end());
		update1(1, k, 1, tmp + 1, lst.ff);

	}

	cout << dp[n] << endl;
}

signed main() {

#ifdef CDuongg
	freopen("bai3.inp", "r", stdin);
	freopen("bai3.out", "w", stdout);
	auto start = chrono::high_resolution_clock::now();
#endif

	ios_base::sync_with_stdio(false);
	cin.tie(nullptr);
	int t = 1; //cin >> t;
	while(t--) solve();

#ifdef CDuongg
	auto end = chrono::high_resolution_clock::now();
	cout << "\n"; for(int i = 1; i <= 100; ++i) cout << '=';
	cout << "\nExecution time: " << chrono::duration_cast<chrono::milliseconds> (end - start).count() << "[ms]" << endl;
#endif

}