#include <bits/stdc++.h>
using namespace std;
void debug_out() { cerr << endl; }
template <class T>
ostream& prnt(ostream& out, T v) {
  out << v.size() << '\n';
  for (auto e : v) out << e << ' ';
  return out;
}
template <class T>
ostream& operator<<(ostream& out, vector<T> v) {
  return prnt(out, v);
}
template <class T>
ostream& operator<<(ostream& out, set<T> v) {
  return prnt(out, v);
}
template <class T1, class T2>
ostream& operator<<(ostream& out, map<T1, T2> v) {
  return prnt(out, v);
}
template <class T1, class T2>
ostream& operator<<(ostream& out, pair<T1, T2> p) {
  return out << '(' << p.first << ' ' << p.second << ')';
}
template <typename Head, typename... Tail>
void debug_out(Head H, Tail... T) {
  cerr << " " << H;
  debug_out(T...);
}
const long long N = 100100;
long long n, k, ans, sum, a[N], b[N];
int main() {
  ios_base::sync_with_stdio(false);
  cin >> n >> k;
  for (long long i = 1; i <= n; i++) cin >> a[i];
  for (long long i = 1; i <= n; i++) b[i] = max(a[i], 0LL);
  for (long long i = 2; i <= n; i++) a[i] += a[i - 1], b[i] += b[i - 1];
  for (long long i = 1; i + k - 1 <= n; i++)
    ans = max(ans, b[i - 1] + a[i + k - 1] - a[i - 1] + b[n] - b[i + k - 1]);
  cout << ans << '\n';
}
