#include <bits/stdc++.h>
#define rep(i,n) for (ll i = 0; i < n; ++i)
#define sz(x) int(x.size())
#define ALL(c) (c).begin(), (c).end()
#define SUM(x) std::accumulate(ALL(x), 0LL)
#define MIN(v) *std::min_element(v.begin(), v.end())
#define MAX(v) *std::max_element(v.begin(), v.end())
#define EXIST(v, x) (std::find(v.begin(), v.end(), x) != v.end())
#define FORV(i, v) for (auto i = v.begin(); i != v.end(); i++)
using namespace std;

typedef int64_t ll;

template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return true; } return false; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return true; } return false; }
const int INF = 1001001001;
const long long INFL = (1LL<<60);
const double eps = (1e-9);


int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);

  int n, k;
  cin >> n >> k;
  vector<ll> a(n);
  rep(i, n) cin >> a[i];

  ll mx = 0;
  for (auto& v : a) {
    if (v > 0) mx += v;
  }

  ll ans = 0;
  ll tmp1 = 0;  // 長さ k の区間で正の数だけ黒にした
  ll tmp2 = 0;  // 長さ k の区間で全部黒の場合
  rep(i, k) {
    if (a[i] > 0) tmp1 += a[i];
    tmp2 += a[i];
  }

  for (int i = k; i < n; i++) {
    if (a[i-k] > 0) tmp1 -= a[i-k];
    tmp2 -= a[i-k];

    if (a[i] > 0) tmp1 += a[i];
    tmp2 += a[i];

    chmax(ans, mx - tmp1 + tmp2);
    chmax(ans, mx - tmp1);
  }

  cout << ans << endl;

  return 0;
}
