#include <bits/stdc++.h>
using namespace std;
using ll = long long;
unsigned euclidean_gcd(unsigned a, unsigned b) {
  if (a < b) return euclidean_gcd(b, a);
  unsigned r;
  while ((r = a % b)) {
    a = b;
    b = r;
  }
  return b;
}
ll ll_gcd(ll a, ll b) {
  if (a < b) return ll_gcd(b, a);
  ll r;
  while ((r = a % b)) {
    a = b;
    b = r;
  }
  return b;
}
class UnionFind {
 public:
  vector<ll> par;
  vector<ll> siz;
  UnionFind(ll sz_) : par(sz_), siz(sz_, 1LL) {
    for (ll i = 0; i < sz_; ++i) par[i] = i;
  }
  void init(ll sz_) {
    par.resize(sz_);
    siz.assign(sz_, 1LL);
    for (ll i = 0; i < sz_; ++i) par[i] = i;
  }
  ll root(ll x) {
    while (par[x] != x) {
      x = par[x] = par[par[x]];
    }
    return x;
  }
  bool merge(ll x, ll y) {
    x = root(x);
    y = root(y);
    if (x == y) return false;
    if (siz[x] < siz[y]) swap(x, y);
    siz[x] += siz[y];
    par[y] = x;
    return true;
  }
  bool issame(ll x, ll y) { return root(x) == root(y); }
  ll size(ll x) { return siz[root(x)]; }
};
long long modpow(long long a, long long n, long long mod) {
  long long res = 1;
  while (n > 0) {
    if (n & 1) res = res * a % mod;
    a = a * a % mod;
    n >>= 1;
  }
  return res;
}
long long modinv(long long a, long long mod) { return modpow(a, mod - 2, mod); }
int main() {
  ll n, k;
  cin >> n >> k;
  vector<ll> z(n);
  ll ans = 0;
  ll gatians = 0;
  ll b = 0;
  for (int i = 0; i < n; i++) {
    cin >> z[i];
    ans += max(z[i], b);
  }
  ll zans = ans;
  for (int i = 0; i < k; i++) {
    zans += min(b, z[i]);
  }
  gatians = zans;
  for (int i = 0; i < n - k; i++) {
    zans -= min(b, z[i]);
    zans += min(b, z[i + k]);
    gatians = max(zans, gatians);
  }
  zans = ans;
  for (int i = 0; i < k; i++) {
    zans -= max(b, z[i]);
  }
  for (int i = 0; i < n - k; i++) {
    zans += max(b, z[i]);
    zans -= max(b, z[i + k]);
    gatians = max(zans, gatians);
  }
  cout << gatians << endl;
}
