#include <bits/stdc++.h>
#pragma GCC optimize("O3", "unroll-loops")
using namespace std;
template<typename Lhs, typename Rhs> bool Min_self(Lhs& lhs, Rhs rhs) { if(rhs < lhs) { lhs = rhs; return true; } return false; }
template<typename Lhs, typename Rhs> bool Max_self(Lhs& lhs, Rhs rhs) { if(rhs > lhs) { lhs = rhs; return true; } return false; }
using ll = long long;
const ll INF = 1'000'000'000'000'000'000;
struct SegTree {
struct Node {
ll val = -INF;
Node() {};
Node(ll _val) : val(_val) {};
Node operator+(const Node& other) const {
Node res;
res.val = max(this->val, other.val);
return res;
}
};
ll n_node = 0;
vector<Node> tree;
void resize(ll n) { n_node = n; tree.resize((n_node << 2) + 10); }
SegTree() {};
SegTree(ll n) { this->resize(n); }
void update(ll node, ll l, ll r, ll idx, ll val) {
if (l == r) {
tree[node].val += val;
return;
}
ll mid = (l + r) >> 1;
if (idx <= mid) update(node << 1, l, mid, idx, val);
else update(node << 1 | 1, mid + 1, r, idx, val);
tree[node] = tree[node << 1] + tree[node << 1 | 1];
}
void Update(ll idx, ll val) {
return update(1, 1, n_node, idx, val);
}
Node query(ll node, ll l, ll r, ll L, ll R) {
if (L <= l && r <= R) return tree[node];
ll mid = (l + r) >> 1;
if (R <= mid) return query(node << 1, l, mid, L, R);
if (L > mid) return query(node << 1 | 1, mid + 1, r, L, R);
return query(node << 1, l, mid, L, R) + query(node << 1 | 1, mid + 1, r, L, R);
}
Node Query(ll l, ll r) {
if (l > r) return Node();
return query(1, 1, n_node, l, r);
}
};
long long solve(int n, int k, int *a, int *b) {
vector<ll> profit(2 * n + 1, 0);
vector<ll> cost(3 * n + 1, 0);
for (ll i = 1; i <= n; ++i) {
profit[i] = profit[i + n] = a[i - 1];
cost[i] = cost[i + n] = cost[i + 2 * n] = b[i - 1];
}
for (ll i = 1; i <= 3 * n; ++i) {
cost[i] += cost[i - 1];
}
auto get_cost = [&] (ll pos) -> ll {
return cost[pos + k - 1] - cost[pos - 1];
};
vector<ll> dp(2 * n + 1, -INF);
SegTree st(2 * n);
for (ll i = 1; i <= 2 * n; ++i) {
st.Update(i, INF); // remove inf
dp[i] = profit[i] - get_cost(i);
if (i > k) {
st.Update(i - k, cost[i - 1]);
}
Max_self(dp[i], st.Query(max(1ll, i - n + 1), i - k).val - get_cost(i));
Max_self(dp[i], st.Query(max(1ll, i - k + 1), i - 1).val + cost[i]);
st.Update(i, dp[i] - cost[i + k - 1]);
}
ll res = 0;
for (ll i = 1; i <= 2 * n; ++i) {
Max_self(res, dp[i]);
}
return res;
}
#ifdef LOCAL
int main() {
int T; assert(scanf("%d", &T) == 1);
for(int t = 0; t < T; t++) {
int N, K; assert(scanf("%d%d", &N, &K) == 2);
int *A = new int[N];
int *B = new int[N];
for(int i = 0; i < N; i++) assert(scanf("%d", &A[i]) == 1);
for(int i = 0; i < N; i++) assert(scanf("%d", &B[i]) == 1);
printf("%lld\n", solve(N, K, A, B));
delete[] A;
delete[] B;
}
return 0;
}
#endif
