#include <bits/stdc++.h>
using namespace std;
using i64 = long long;
using ll = long long;
#define pb emplace_back
#define X first
#define Y second
#define AI(i) begin(i), end(i)
template<class T> bool chmax(T &a, T b) { return a < b && (a = b, true);}
template<class T> bool chmin(T &a, T b) { return b < a && (a = b, true);}
#ifdef KEV
#define DE(args...) kout("[ " + string(#args) + " ] = ", args)
void kout() { cerr << endl; }
template<class T, class ...U> void kout(T a, U ...b) { cerr << a << ' ', kout(b...); }
template<class T> void debug(T l, T r) { while (l != r) cerr << *l++ << " \n"[l==r]; }
#else
#define DE(...) 0
#define debug(...) 0
#endif

const int MAX_N = 300010;
int main() {
	ios_base::sync_with_stdio(0), cin.tie(0);

	auto solve = [&]() {
		int n, K, D;
		cin >> n >> K >> D;

		vector<int> h(n);
		for (int i = 0; i < n; i++) {
			cin >> h[i];
		}

		vector<int> t(n - 1);
		for (int i = 0; i < n - 1; i++) {
			cin >> t[i];
		}

		constexpr i64 INF = 1e18;
		vector<i64> dp(n);

		vector<priority_queue<array<i64, 2>>> f(K);
		vector<i64> offset(K);
		multiset<array<i64, 3>, greater<>> g;

		for (int i = 0; i < K; i++) {
			f[i].push({-INF, n});
			g.insert({-INF, n, i});
		}	

		auto erase = [&](array<i64, 3> a) {
			g.erase(g.find(a));
		};

		auto pop = [&](int idx) {
			auto [cost, r] = f[idx].top();
			g.erase(g.find({cost - offset[idx], r, idx}));
		};

		auto push = [&](int idx) {
			auto [cost, r] = f[idx].top();
			g.insert({cost - offset[idx], r, idx});
		};
		
		for (int i = 0; i < n; i++) {
			while (g.begin()->at(1) < i) {
				int idx = g.begin()->at(2);
				pop(idx);
				f[idx].pop();
				push(idx);
			}
			int idx = i % K;
			pop(idx);
			offset[idx] += D;
			push(idx);
			if (i == 0) {
				dp[0] = h[0];
			} else {
				dp[i] = g.begin()->at(0) + h[i];
			}
			if (i < n - 1) {
				pop(idx);
				i64 cost = dp[i], r = i + t[i];
				f[idx].push({cost + offset[idx], r});
				push(idx);
			}
		}

		debug(dp.begin(), dp.end());

		cout << dp[n - 1] << '\n';
	};

	solve();
}