#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, k;
  cin >> n >> k;
  long a[n];
  for (int i = 0; i < n; i++) {
    cin >> a[i];
  }
  long acc_a[n + 1], acc_b[n + 1];
  acc_a[0] = acc_b[0] = 0;
  for (int i = 1; i <= n; i++) {
    acc_a[i] = acc_a[i - 1] + a[i - 1];
    acc_b[i] = acc_b[i - 1] + max(0l, a[i - 1]);
  }
  long ans = 0;
  for (int i = k; i <= n; i++) {
    ans = max(ans, acc_b[n] - acc_b[i] + acc_a[i] - acc_a[i - k] +
                       acc_b[i - k] - acc_b[0]);
  }
  cout << ans << endl;
  return 0;
}
