#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<int, int> pii;
#define pb push_back
#define all(a) a.begin(), a.end()
#define sz(a) ((int)a.size())
const int mod = 998244353, N = 100005, K = 1000;


deque<pair<ll, int>> dq;
priority_queue<pair<ll, int>> pq[K];
vector<pair<ll, int>> eve[N];
ll n, k, d;
int t[N];

void insert_dq(ll x, int i) {
    for (int j = i; j + k - 1 <= i + t[i]; j += k, x += d)
        eve[j].pb(pii(x, j + k - 1));
}

void upd_dq(int now) {
    for (auto [x, y] : eve[now]) {
        while (!dq.empty() && dq.back().first <= x)
            dq.pop_back();
        dq.emplace_back(x, y);
    }
    while (!dq.empty() && dq.front().second <= now)
        dq.pop_front();
    for (auto [x, y] : eve[now + 1]) {
        while (!dq.empty() && dq.back().first <= x)
            dq.pop_back();
        dq.emplace_back(x, y);
    }
}

ll get_dq() {
    return dq.empty() ? -1ll << 40 : dq.front().first;
}

void insert_pq(int id, ll x, int i) {
    pq[id].push(pii(x, i + t[i]));
}

ll get_pq(int id, int now) {
    while (!pq[id].empty() && pq[id].top().second < now)
        pq[id].pop();
    return pq[id].empty() ? -1ll << 40 : pq[id].top().first;
}

int h[N];

int main() {
    ios::sync_with_stdio(false), cin.tie(0);
    cin >> n >> k >> d;
    d *= -1;
    for (int i = 0; i < n; ++i)
        cin >> h[i];
    for (int i = 0; i < n - 1; ++i)
        cin >> t[i];
    if (k > K) {
        ll dp = h[0];
        insert_dq(dp, 0);
        upd_dq(0);
        insert_pq(0, dp + t[0] / k * d, 0);
        for (int i = 1; i < n; ++i) {
            dp = max(get_dq() + h[i], get_pq(0, i) + h[i]);
            if (i == n - 1)
                break;
            insert_dq(dp, i);
            upd_dq(i);
            insert_pq(0, dp + t[i] / k * d, i);
        }
        cout << dp << '\n';
    }
    else {
        ll dp = h[0];
        insert_pq(0, dp, 0);
        for (int i = 1; i < n; ++i) {
            dp = -1ll << 40;
            for (int j = 0; j < k; ++j) {
                dp = max(dp, get_pq(j, i) + (i - j) / k * d + h[i]);
                //cout << "D" << j << ' ' << dp << '\n';
            }
            //cout << i << ' ' << dp << '\n';
            if (i == n - 1)
                break;
            insert_pq(i % k, dp - i / k * d, i);
        }
        cout << dp << '\n';
    }
}