/*
Author : DeMen100ns (a.k.a Vo Khac Trieu)
School: Ho Chi Minh City University of Science
*/

#include <bits/stdc++.h>
#define endl '\n'

#define int long long

using namespace std;

template<typename T> int SIZE(T (&t)){ return t.size(); } template<typename T, size_t N> int SIZE(T (&t)[N]){ return N; } string to_string(char t){ return "'" + string({t}) + "'"; } string to_string(bool t){ return t ? "true" : "false"; } string to_string(const string &t, int x1=0, int x2=1e9){ string ret = ""; for(int i = min(x1,SIZE(t)), _i = min(x2,SIZE(t)-1); i <= _i; ++i){ ret += t[i]; } return '"' + ret + '"'; } string to_string(const char* t){ string ret(t); return to_string(ret); } template<size_t N> string to_string(const bitset<N> &t, int x1=0, int x2=1e9){ string ret = ""; for(int i = min(x1,SIZE(t)); i <= min(x2,SIZE(t)-1); ++i){ ret += t[i] + '0'; } return to_string(ret); } template<typename T, typename... Coords> string to_string(const T (&t), int x1=0, int x2=1e9, Coords... C); template<typename T, typename S> string to_string(const pair<T, S> &t){ return "(" + to_string(t.first) + ", " + to_string(t.second) + ")"; } template<typename T, typename... Coords> string to_string(const T (&t), int x1, int x2, Coords... C){ string ret = "["; x1 = min(x1, SIZE(t)); auto e = begin(t); advance(e,x1); for(int i = x1, _i = min(x2,SIZE(t)-1); i <= _i; ++i){ ret += to_string(*e, C...) + (i != _i ? ", " : ""); e = next(e); } return ret + "]"; } template<int Index, typename... Ts> struct print_tuple{ string operator() (const tuple<Ts...>& t) { string ret = print_tuple<Index - 1, Ts...>{}(t); ret += (Index ? ", " : ""); return ret + to_string(get<Index>(t)); } }; template<typename... Ts> struct print_tuple<0, Ts...> { string operator() (const tuple<Ts...>& t) { return to_string(get<0>(t)); } }; template<typename... Ts> string to_string(const tuple<Ts...>& t) { const auto Size = tuple_size<tuple<Ts...>>::value; return print_tuple<Size - 1, Ts...>{}(t); } void dbgr(){;} template<typename Heads, typename... Tails> void dbgr(Heads H, Tails... T){ cout << to_string(H) << " | "; dbgr(T...); } void dbgs(){;} template<typename Heads, typename... Tails> void dbgs(Heads H, Tails... T){ cout << H << " "; dbgs(T...); } 
#define dbgv(...) cout << to_string(__VA_ARGS__) << endl;
#define dbg(...) cout << "[" << #__VA_ARGS__ << "]: "; dbgv(__VA_ARGS__);
#define dbgr(...) dbgr(__VA_ARGS__); cout << endl;
#define dbgm(...) cout << "[" << #__VA_ARGS__ << "]: "; dbgr(__VA_ARGS__);

const int N = 1e5 + 5;
const long long INF = numeric_limits<long long>::max() / 2;
const int MAXA = 1e9;
const int B = sqrt(N) + 5;

int n, k, d;
int a[N], dp[N], h[N], t[N];
vector <int> sum[N];
multiset <int> cur[N];
vector <int> er[2 * N];
int seg[4 * N];

void upd(int id, int l, int r, int u, int v, int val){
    if (l > v || r < u) return;
    if (l >= u && r <= v){
        seg[id] = max(seg[id], val);
       // lazy[id] = max(lazy[id], val);
        return;
    }
    //down(id);
    
    int mid = (l + r) >> 1;
    upd(id << 1, l, mid, u, v, val);
    upd(id << 1 | 1, mid + 1, r, u, v, val);
}

int get(int id, int l, int r, int pos){
    if (l == r) return seg[id];
    
    int mid = (l + r) >> 1;
    if (pos <= mid) return max(seg[id], get(id << 1, l, mid, pos));
    else return max(seg[id], get(id << 1 | 1, mid + 1, r, pos));
}

void case1(){
    for(int i = 0; i < n; ++i){
        int l = i + 1, r = i + t[i + 1];
        // if (i / k > 0){
        //     sum[i % k][i / k] += sum[i % k][i / k - 1];
        // }
        for(int val : er[i]){
            cur[i % k].erase(cur[i % k].find(val));
        }

        int val;
       // dbgm(i, (i / k) * -d, cur[i % k], h[i + 1])
        if (i > 0) val = (i / k) * -d + (*prev(cur[i % k].end())) + h[i + 1];
        else val = h[1];
       // dbgm(i, val)
        if (i == n - 1){
            cout << val;
            return;
        }
        for(int j = 0; j < k; ++j){
            int lk = (l - 1) / k, rk = r / k;
            if ((l - 1) % k > j) ++lk;
            if (r % k < j) --rk;

            //dbgm(j, l, r, lk, rk)

            if (lk > rk) continue;
            //dbgm(val + lk * d)
            cur[j].insert(val + lk * d);
            er[(rk + 1) * k + j].push_back(val + lk * d);
           // dbg((rk + 1) * k + j)
            // pol[j][lk] -= d;
            // if (rk + 1 < pol[j].size()) pol[j][rk + 1] += d;
            // sum[j][lk] += lk * d;
            // if (rk + 1 < sum[j].size()) sum[j][rk + 1] -= lk * d;
        }
    }
}

void case2(){
    fill_n(seg, 4 * n + 1, -INF);
    upd(1, 1, n, 1, 1, 0);
    for(int i = 1; i < n; ++i){
        dp[i] = get(1, 1, n, i) + h[i];
        for(int l = i, r = min(i + k - 1, i + t[i]), v = 0; l <= i + t[i]; l += k, r = min(r + k, i + t[i]), v += d){
            //cout << i << " : " << l << " " << r << " -> " << dp[i] << " " << v << endl;
            upd(1, 1, n, max(i + 1, l), r, dp[i] - v);
        }
    }
    dp[n] = get(1, 1, n, n) + h[n];
    cout << dp[n];
}

void solve(){
    cin >> n >> k >> d;
    for(int i = 1; i <= n; ++i) cin >> h[i];
    for(int i = 1; i < n; ++i) cin >> t[i];
    
    if (k < B / 3) case1();
    else case2();
}

signed main(){
    ios_base::sync_with_stdio(0); cin.tie(0);

    int t = 1; // cin >> t;
    for(int test = 1; test <= t; ++test){
        solve();
    }
}