#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[n + 1];
  acc[0] = 0;
  for (int i = 1; i <= n; i++) {
    acc[i] = acc[i - 1] + a[i - 1];
  }
  long max_acc = 0;
  int index = 0;
  for (int i = k; i <= n; i++) {
    if (max_acc < acc[i] - acc[i - k]) {
      max_acc = acc[i] - acc[i - k];
      index = i - k;
    }
  }
  long ans = 0;
  if (max_acc == 0) {
    long min_acc = 10000000000000007;
    acc[0] = 0;
    for (int i = 1; i <= n; i++) {
      acc[i] = acc[i - 1] + max(0l, a[i - 1]);
    }
    for (int i = k; i <= n; i++) {
      if (min_acc > acc[i] - acc[i - k]) {
        min_acc = acc[i] - acc[i - k];
        index = i - k;
      }
    }
  } else {
    ans = max_acc;
  }
  for (int i = 0; i < k; i++) {
    a[i + index] = 0;
  }
  for (int i = 0; i < n; i++) {
    if (a[i] > 0) ans += a[i];
  }
  cout << ans << endl;
  return 0;
}
