#include <bits/stdc++.h>
template <typename T>
void MACRO_VAR_Scan(T& t) {
  std::cin >> t;
}
template <typename First, typename... Rest>
void MACRO_VAR_Scan(First& first, Rest&... rest) {
  std::cin >> first;
  MACRO_VAR_Scan(rest...);
}
template <typename T>
void MACRO_VEC_ROW_Init(int n, T& t) {
  t.resize(n);
}
template <typename First, typename... Rest>
void MACRO_VEC_ROW_Init(int n, First& first, Rest&... rest) {
  first.resize(n);
  MACRO_VEC_ROW_Init(n, rest...);
}
template <typename T>
void MACRO_VEC_ROW_Scan(int p, T& t) {
  std::cin >> t[p];
}
template <typename First, typename... Rest>
void MACRO_VEC_ROW_Scan(int p, First& first, Rest&... rest) {
  std::cin >> first[p];
  MACRO_VEC_ROW_Scan(p, rest...);
}
template <typename T>
inline T CHMAX(T& a, const T b) {
  return a = (a < b) ? b : a;
}
template <typename T>
inline T CHMIN(T& a, const T b) {
  return a = (a > b) ? b : a;
}
void CHECKTIME(std::function<void()> f) {
  auto start = std::chrono::system_clock::now();
  f();
  auto end = std::chrono::system_clock::now();
  auto res = std::chrono::duration_cast<std::chrono::nanoseconds>((end - start))
                 .count();
  std::cerr << "[Time:" << res << "ns  (" << res / (1.0e9) << "s)]\n";
}
using ll = long long;
using ull = unsigned long long;
constexpr ll INFINT = 1 << 30;
constexpr ll INFINT_LIM = (1LL << 31) - 1;
constexpr ll INFLL = 1LL << 60;
constexpr ll INFLL_LIM = (1LL << 62) - 1 + (1LL << 62);
constexpr double EPS = 1e-7;
constexpr ll MOD = 1000000007;
constexpr double PI = 3.141592653589793238462643383279;
signed main() {
  std::ios::sync_with_stdio(false);
  std::cin.tie(0);
  ;
  ll n, k;
  MACRO_VAR_Scan(n, k);
  ;
  std::vector<ll> a(n);
  for (auto& i : a) std::cin >> i;
  ;
  std::vector<ll> c(n, a[0]);
  for (ll i = (1); i < (n); ++i) {
    c[i] = c[i - 1] + a[i];
  }
  std::vector<ll> b(a);
  for (ll i = 0; i < ll(n); ++i) {
    if (b[i] < 0) b[i] = 0;
  }
  for (ll i = (1); i < (n); ++i) {
    b[i] += b[i - 1];
  }
  b.push_back(b[n - 1]);
  ll max = 0;
  for (ll i = (k - 1); i < (n); ++i) {
    ll s = std::max(0LL, c[i] - ((i - k + 1 >= 0) ? c[i - k + 1] : 0));
    ll t = ((i - k >= 0) ? b[i - k] : 0);
    ll r = b[n] - b[i];
    CHMAX(max, s + t + r);
  }
  std::cout << max;
  std::cout << "\n";
  ;
  return 0;
}
